Which Type of Tensiometer do I Need?

As followers of these rants know, Fisher Scientific stopped offering its Tensiomat Tensiometer about a year ago. As a tensiometer manufacturer, we at CSC Scientific were very interestedin this and have tried to let the world know that we might be able to help with things such as replacement rings, trade-ins and the like.

In discussing alternatives with Tensiomat users, we are often asked, “if I am going to replace my tensiometer, which one should I get?”

Let's explore the alternatives and compare their respective capabilities.

The simplest tensiometer has a duNouy Ring hanging by a hook from a level arm. This is a staple for measuring surface tension in simple liquids as well as measuring interfacial tension between oil and water. As the liquid thickens, an option with the ring rigidly fixed to the lever arm is helpful. This version can also measure the interfacial tension between two liquids in a downward direction.

Beyond these classic models, which cost in the $4,000 range, are the starting electronic balance-driven digital versions that can perform the duNouy ring tests as well as the Wilhelmy Plate technique. This level of tensiometer works well for static surface tension analysis. Depending on the test procedure’s degree of automation, these digital tensiometers cost between $6,500 and $10,000

As the testing requirements expand to include as the likes of Lamella length, sedimentation rates and temperature studies, automation and computer analysis; tensiometer capabilities grow as well. Instruments that require such features range from $12,000 to $20,000. The cost levels usually depend on the number of alternative techniques included.

As requirements expand to include determining dynamic surface tension, powder contact angle, powder wettability and dynamic surface tension, the cost level can increase to the $40,000 plus range.

When the requirement is for just surface tension, the basic units can usually meet the needs for periodic testing. However, wth high test volumes and expanded test functions, the higher-cost units become important alternatives.

Our affiliate Scientific Gear constructed a capability comparison table to help determine the type of instrument needed to best support an application. Click on the button for a copy.

 

We are available to discuss your specific application and help identify the instrument that will most effectively meet your needs. We hope this short review will be helpful in understanding the tensiometer alternatives and their particular capabilities.

I remain a continually astonished,

Art

P.S. You can subscribe to these raves and rants and be notified when a new one has been conjured up.

Who Beats Up Your Bostwick?

Sometimes we encounter a product that is so simple and rugged that it would be tempting to deem it indestructible. Consider a stainless steel trough with a gate and etched numbers on the bottom. Seems simple and the stainless would make it tough, right? That is not the case, but it has survived nearly unchanged for more than 85 years.

 Just described the Bostwick Consistometer, which CSC has been making since the beginning.

 You may familiar with some of its uses such as checking sauces, toppings, slurries, paints and other types of flowing materials. It is used in many challenging environments such as:

• The tropics

• Pristine labs

• Production lines

• Airports in the Winter when de-icing airplane wings and bodies

• Anywhere else you want to check a process that makes a flowing product

Ensuring proper measurement requires cleaning after testing. Detergent, high-temperature washers, solvent baths and other cleaning/scouring media are used.

The Bostwick Stands Up

Ingenuity is helpful in finding ways to destroy the bubble level that indicates when the set-up is ready for testing. Using King Kong-like staff members, you can trash the gate mechanism. Further, with King Kong or mechanical vises, the Bostwick can be bent beyond recognition. However, in normal use it is difficult to wreck a Bostwick.

Nonetheless, production operators drop Consistometers on concrete floors, toss them from great distances into cleaning sinks or otherwise lose physical control of their Bostwicks. Like prisoners facing repeated interrogation, Bostwicks eventually succumbs. Typicaly, damage involves a bent support deck for the leveling screws along with destruction of the leveling screw supports – fatal failures, no longer will it measure Consistency.

We at CSC Scientific get many of these sent to us for partial reconstruction.

Recently, a long-time friend and customer gave us a design to highly challenge these King Kong operators. Almost had to throw the modified Bostwick under a bus or forklift to cause fatal failures. We call this design the “Abuse Protection Option.”

Click the button to review the results and how the Abuse Protection Option (APO)may thwart prospective Bostwick destroyers.

 

I hope this has been at least a little fun. If you have recurring fatal failures, perhaps you should consider an ABO on your next Bostwick.

I am still searching to useful insights on test equipment secrets.

Art

Is Sieve Calibration Really the Holy Grail? -- Part I: Certification

Sieve calibrationis the final step in determining whether processes yield suitable end results. In other words:

• Is your concrete going to be strong enough?

• Will you chocolates taste right?

• Will your washing powder flow and dissolve as advertised?

• Is there dangerous residue in your pill stock?

• Will the “frack sand” keep the fractures open?

• Is my salt of the correct grade?

If these are not correct, serious consequences could result (e.g. spoiled product, returned batches, rework or scrap).

These are the particle-size issues for which we test, frequently using woven wire mesh sieving techniques. For a long time, I've made sporadic attempts to understand how to ensure that tests really represent particle distribution. Many phenomena can affect these determinations.

I have decided to undertake clarifying this murky process. There are inherent irregularities in most woven materials. Regarding woven wire mesh used in sieves, standards organizations attempt to determine the acceptable range of these irregularities and then set acceptable variation limits.

Mesh problems also arise from the testing process as well as cleaning and various forms of abuse. How do we determine if these processes affect sieve performance?

By means of illustration, I offer a particle’s perspective, the particle which I've named Pequeño. He encounters a sieve, undergoes a test, is cleaned out of an undersized hole and attacks several calibration operations.

Pequeño is doing this in Four episodes, the first of which we will explore now and the others in later blogs:

• Bouncing around in a test

• Getting cleaned

• Beating the calibration

***

Episode I: Certification

I am Pequeño, a particle with a passion to get through any sieve and not be amongst the particles retained.

My story begins as I observe Brad, a professional sieve certifier, at work squinting through a microscope at a series of nearly square openings bounded by sections of wire that span the entire sieve. In one direction, the wires go straight across the sieve (Weft). In the other direction, the wires alternately go over and under the straight wires (Warp).

I'm from a large family of very small (about 150 micron) siblings. Brad is working on a number 100 8-inch diameter sieve with 150-micron nominal apertures, holes or openings (they can be called any of these). It has about 500,000 of these openings. It should be easy for me to migrate to the next sieve.

Brad is inspecting and measuring  200 of these  holes (about 0.04% of the total). He is measuring the wire in each as well as one side along the weft and one side along the warp. When finished, he will apply ASTM-specified formulae and determine if the sieve meets specifications.

Within the acceptable specs for these 200 openings, the average could be as large as 156.6 microns. There should be no problem of my getting through openings that size. However, this average could be as low as 143.4 microns.This could finish me, but the another specified dimension is the 193-micron maximum allowable size of an individual opening.

If I look around enough, I should even be able to get through a sieve that Brad calculates as the minimum. Remember, Brad only measured 1-in-2500 openings.

If his task was to certify that the sieve meet the highest standard -- the Calibration Sieve Category -- he would apply a reasonably tight standard deviation to his measurements. This would reduce my chances of getting through on the small average, which would only make it more of a challenge to find an opening through which I can pass.

In fact, I even have a shot at getting through a sieve with the next smallest designation (number 120 with 125 microns nominally sized holes). The allowable maximum of any individual hole measured can be 168 micron -- an easy transit for me.

I like the theoretical odds of feeding my passion of getting through my size and smaller sieves (hate to be in the retained category). In fact, I might even nvite some of my larger siblings to join me.

In my next visit, I'll take you with me on some real production tests that use the sieve that Brad measured and professionally certified.

Until then,

Pequeño

***

I hope you found this entertaining and somewhat informative.Take a look at some sieve alternatives.

 

Thanks for your attention, I remain distracted, mystified but still swinging,

Art

P.S. If these musings on lab test equipment are interesting, subscribe  above.

 

Why Do I Get Inconsistent Moisture Test Results?

“Why are my Moisture Test results inconsistent?” 

That is an issue for many of you who test for moisture. We discussed the complexities and multiplicity of issues involved with moisture content determination in our “Loss-on Drying Moisture Analysis and other Moisture Mysteries” series.

In addition to intrinsic properties of test samples that may adversely affect moisture testing systems, automatic equipment parameter set-up, operator oversights and sample handling contribute to seemingly intractable moisture test result inaccuracies.

Common test sample vagaries include:

1. Volatiles other than water that are released at close to the same vapor pressure as water evaporation.
2. Strange conditions of entrapped moisture that release water at capricious times.
3. Samples not representative of the principal batch

 

It is important to determine if these test sample quirks are responsible, because test protocols may require changing. Variations can also be minimized by running more tests to statistically reduce variation effects. In some cases, changes in test methods may be needed (i.e. Karl Fischer rather than Loss-on-Drying).

While trouble-shooting such problems, it is important to check automatic setting level and operation, which determine when a test is completed. With the Loss-on Drying method, these settings relate to measuring sample weight changes. If the instrument is set to stop too soon, the weight-loss curve will slope steeply and the moisture result will be subject to irregular variations from test to test. If the end-of-test calculation is based upon too small of a weight change, there is a potential for burning the sample -- another cause of inconsistency.

Similar problems can arise if widely different test-to-test sample weights are used in a timed test environment.

Another source of inconsistent analysis can be that a small amount of moisture requires detection. A small amount of sample and a very sensitive balance are frequently used for this type of test. Operators must carefully follow test procedures or the balance’s high sensitivity will yield wide result variations from test to test ( Often A switch to the Karl Fischer Method will Solve this Problem).

As equipment manufacturers, we will ultimately consider the possibility of instrument malfunctions. Our experience with instrument service leads us to either clear instrument failure or consistent high or low results signaling equipment problems and not just inconsistent results.

Our troubleshooting protocols require duplicating clients’ problems in our lab. When we cannot, experience leads us to consider environmental conditions at our customers' facilities. Frequently, we find electrical power conditions to be responsible. Special power-conditioning equipment will usually solve this problem.

On occasion, we cannot find the sources of variation.

In summary, issues relating to test sample properties and/or or incorrect test parameters normally yield inconsistent results. Occasionally it is operator error. However, on rare occasions, test site environmental conditions are responsible.

Sometimes it requires painstaking investigation to find the cause. When found, we can usually then develop workable solutions.

I hope this sheds some light on the sources of inconsistent test results.

As usual, there is still a bit of witchcraft and folklore needed to solve the more elusive measurement  problems.

Still trying to get answers, I remain a puzzled,

Art

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Why Calibrate a CSC DuNouy Tensiometer?

Within the catalog of questions we are asked is a  category related to Calibrating duNouy Ring Tensiometers. The subject matter ranges from how, why and what is proven?

I guess the immediate and wise-assed answers are:

• To see if the Tensiometer is working.

• To determine if it is working correctly

• Because it gives a reference for ISO traceability

Some of the calibration schemes pertain specifically to the unique design of the CSC Tensiometer and its application of torsion balance concepts.

Our tensiometers determine vertical force by measuring the twist or torsion in a wire. Starting from an equilibrium point where a our scale dial is at zero;

      1.  We pull a duNouy ring through a liquid surface

      2. This twists the wire as it resists the surface tension force and

      3.  We measure the amount of twist or torsion in the wire needed to            pull the ring completely through the surface.

A calibration procedure is needed to produce a measurement in accepted units of surface tension (dynes/cm),as well as obtaining a reading that relates to a traceable measure or value. Thus, the real answer is all three of the above;  the Tensiometer is working, working correctly and the results are traceable.

I shall describe the procedure which assures that a test reading is accurate.

The procedure goes as follows:

• Set up the Tensiometer so  the indicator is on the “0” line in the mirror and the dial reads Zero. Like a Seesaw or Teeter Toder,in balance with equal sized kids ( Ralph and Rachel) on either side. The ring (Ralph) on “teeter” side and the arm (Rachel) on the “totter” side.

• Now we add a known weight to the ring which pulls down the indicator. (We handed Ralph some free weights).

• We now turn our dial until the indicator goes back to Zero, (We give Rachel  some stones until until it balanced again).

• At this point we apply a magical formula that lets a wizard tell us what the dial should read if every thing is in correct balance.

• We reconcile any difference between that number and the dial reading by adjusting the arm length. Thus, the wizard says Ralph should have more weights or  that Rachael should move in or out on her side of the “totter” until the Seesaw balances again.

• Now we know that for a given weight, along with Ralph’s and Rachel’s specific position, the seesaw will be in balance. In other words, we know how much force will be needed to move the dial by one dyne. This magical formula makes the translation of the weight added to the number the dial should read.

We have a short video that shows how this calibration process works. You can get to it by clicking on the bubble.

 

I had fun putting this together and  hope it simplified understanding of  the tensiometer calibration process (except for the magical formula the basis of which is a designer’s secret).

Let me know what your interests are and we'll try to rail about them. You can do this by commenting below or by emailing me at artgatenby@gmail.com

I thank you for following my rants.

A befuddled as usual,

Art

P.S.  Hope you enjoyed meeting Ralph and Rachel.  By the way sign up and subscribe to our Test Equipment Rants.

Karl Fischer Moisture – Answers to Questions We Get Asked

When People are first introduced to the Karl Fischer Moisture Determination Method, eyes glaze over and we can perceive a mental “Why did I Ask?”

If you have any history with moisture analysis, you will have found, that for some applications, the Karl Fischer Titration Method is the best and sometimes the only way to get an accurate moisture measurement.

Most non-chemists react to the thought of titrations with “Not for me – do I have to do this?” Even the chemical formula for the Karl Fischer reactionis mind blowing.

However, these days most of the pain is removed with automatic Karl Fischer instruments such as our Aquapal III, that make conducting Karl Fischer tests quite simple. There are still times when your not sure if the equipment is reading correctly or when it gives arcane messages like "Over Titration" that you feel panic. A host of other subtle problems bring on the question “What does this Mean?”

Recently Hank Levi, a colleague of ours at Scientific Gear, developed a list of 20 questions that are periodically asked. He also developed concise answers. They are questions like;

• Why won't my instrument get to the Ready Mode?
• What kind of reagent should I use?
• Is my instrument giving me correct results?
• How much sample should I use?

We would like to share these with you. If you click on the button you can down-load the full list of  Karl Fisher questions and answers.

Hank tells us that some of his customers post this list in the lab where it is available for reference at any time to the staff conducting Karl Fischer moisture determinations.

Maybe this will help reduce trepidation about Karl Fischer and help get good repeatable results.

We hope that you check out this list and that it is useful to you. Again thanks for visiting.

I remain a wary respectful friend of Karl Fischer,

Art

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Sieves – Old and New QC Issues

In April, we published an article in "Powder-Bulk Solids" comparing certification process veracity with a sieve calibration process using calibrated glass microspheres (or beads). The certification process merely indicates that a sieve mesh conforms to a standard that has a wide tolerance regarding mesh openings. It is performed on a small number of openings. On the other hand, calibration using the calibrated beads results in a number representing the mean opening -- a result generated by actually performing a test encompassing at least 80% of the mesh openings.

Given that the calibration process highlights the actual performance of a given sieve, we recommended that QC departments switch to a calibration method to determine the suitability of the sieves used in tight-tolerance situations. This requires a different mindset from test sieve manufacturers as well as QC departments responsible for controlling sieve processes.

We recently had a real-life example of the the difference between actual sieve performance and certification statistics. A customer recently acquired four 45 micron (#325) ASTM certified sieves. Given that their manufacturing process was critical, they decided to check the four sieves with calibration beads. The results on each sieve showed a mean aperture of 49 microns. Because the certification spec allowed a variation of up to 3 microns in average opening size (allowing up to 48 microns in average opening) They returned the sieves to the manufacturer for re-certification. All four sieves passed. The customer also had them double-checked by an outside laboratory. Each of the four sieves tested the same; consistent with a real-world sample as well as bead calibration results.

What to do? --- Whom to believe? --- What ARE these sieves?

In light of this, let's consider the most recent ASTM specification (ASTM E 11-09). The customer's sieves were 8 inches in diameter, which represented approximately 15 million openings. The most exact ASTM certification requires examining only 1,000 openings ---- less than .01% of the number in an 8-inch #325 sieve. For these 1,000 measured openings, the maximum allowable average opening size variation is 3 microns with an allowable maximum opening of 67 microns. Given that the bead calibration produced a mean opening of 49 microns, the customer felt that the sieve was out of spec compared to the maximum allowable average of plus three microns (45+3 ) of the observed 1,000 openings. Note that these statistics are all based on measurements and not on actual sieve test performance.

The bead calibration tolerance is about 1 micron in mean opening resulting from a sieve test using a calibrated sphere sample.

This real-life situation makes it clear that certification, while an insurance policy of some value, does not predict a sieve’s actual performance. It does nothing more than sample some openings and determine if the sieve mesh is within prescribed tolerances.

Calibration performs a live sieve test and yields the actual results.This leads us to the conclusion that calibration with glass spheres is the optimal procedure for determining the suitability of a test sieve as well as checking and controlling a process.

We can compare mesh sieve performance to the results on the same sample, but predicting it can only be accomplished by conducting an actual sieve test using a precise sample such as Calibration Beads.

To date, calibrated spheres are the best method for this and for determining the actual calibration of any test sieve.

As with most of the things I rail about here, real world conditions often lead to confusion about theory and when analyzed question established practice.

I hope this has been helpful.  Call me at 703-876-4030 if you want to discuss the certification/calibration dichotomy.

Art

P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for e-mail notice by jotting your address in the box just to the right of the title.

 

Loss-on Drying and Other Moisture Mysteries - Part V: Drying

Just over six months ago, I began this journey explaining the simplest approach to measuring or determining moisture: Loss-on Drying. Little did I know how involved and esoteric it would become.

This voyage has taken me down mysterious paths through spooky theories, back to age-old chemistry concepts and into the vagaries of thermodynamics related to evaporation, vapor pressure, bound water and water activity. I have come full-circle; back to explaining Loss-on Drying -- a form of drying that I had assumed would be the simplest of all.

I thought the first four topics [evaporation, vapor pressure, bound moisture, water activity] were tough, complex, confounding and less-than-obvious. Drying -- defined as “the mass-transfer process of removing water (or other solute) by evaporation from a solid, semi solid or liquid” -- seemed easy.

As is often the case, reality makes “easy” a non-operative word. Such has turned out to be so with respect to the issue of drying.

To begin, there is the process in which heat is transferred to create a temperature in a solid that evaporates moisture from the surface and causes it to migrate from the inside outward. This internal migration occurs through several mechanisms such as diffusion, capillary action and the internal pressure created by shrinkage. It is not as simple as hanging laundry on a clothes line to dry on a breezy, sunny day.

Firstly, there is the initial and underlying issue of product classification. Here are some examples:

1. Non-hygroscopic Capillary Porous Solids: These are materials such as sand, crushed minerals, certain crystals, polymer particles and some ceramics. They have recognizable pore space filled with liquid, little bound moisture and do not shrink on drying.

2. Hygroscopic Porous Solids: Clay, molecular sieves, wood, textiles, silica gels, alumina and zeolites are examples. They are characterized by clearly seen pore space, physically bound moisture and shrinkage in the early stages of drying.

3. Colloidal (non Porous) Solids: Examples include soap, glue, polymers like nylon and various food products. There is no pore space and all moisture -- except that on the surface -- is physically bound.

There are other less-common classifications and combinations as well.

In the drying process, the rate of moisture removal varies widely between these classifications. In some, the rate is linear throughout. In others, the removal-rate is high at the beginning and diminishes as drying progresses [as illustrated in the dreaded drying-rate curves]. The principles of evaporation, equilibrium pressure, vapor pressure, partial pressure, temperature, relative humidity, dew point, moisture sorption isotherms and ideal gas laws all apply. As you may remember, some of these concepts have effect in other sections of the Moisture Mysteries Series. They all apply to this concluding phenomenon of drying, to which in the beginning I naively referred as just plain drying.

Most products from today's industry undergo drying at some stage. For example, drying is an important element in a wide range of products such a food, pharmaceuticals, lumber, paper, fiberboard and a host of chemical products. In fact, approximately 10% of the energy consumption in the US and Canada is directly related to production drying.

All of the issues that stretched my thought process are present with the development of production systems. Consequently, dryer designs are not universal across product classifications because of the inherent complexities in the drying process. Production drying systems are developed for specific products. These include convection, belt, fluid bed, rotary, spray, flash and drum dryers.

One of the more difficult issues is to get at is the bound water. Among other techniques to deal with this is freeze-drying. Additionally, there are mechanical methods of removing moisture [e.g. centrifuging] that are referred to as dewatering rather than drying.

A compromise is often sought between the cost of transportation (lower moisture) and the cost of drying. Further, the level of drying is often a measure of a product’s suitability for market -- i.e. color, flavor, shrinkage, palatability and cracking. To check the effectiveness of these processes in meeting the diverse objectives, the moisture content after drying needs to be determined. The most frequently used technique of moisture determination is Loss-on Drying. That was the reason for this series of articles that sought to explain the factors of drying.

The Loss-on Drying moisture measurement process involves all issues and considerations concerned with production drying. People regularly ask us, “at what temperature should we run the test and for how long?” This discussion of drying should help them understand why we reply “It depends”.

I hope this “Loss-on Drying and Other Moisture Mysteries” series has been interesting and useful. Also I hope it was fun.

Now that I have finished Part V, the last in the series, I remain more astonished than ever with the mysteries of the test equipment world.

Thanks for visiting.

Art

P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for email notice by entering your address into the box just to the right of the title.

Why Not A Bostwick Consistometer Calibration Standard?

Customers want Bostwick Consistometer Calibrations.

When told that CSC Scientific does not calibrate Bostwick Consistometers, people ask . “Then how can I calibrate my consistometer and where can I get a calibration standard?”.

We recommend sampling the selected product to be measured  using the Bostwick Consistometer. The sample should represent your product in its ideal state. The temperature should be carefully recorded and a test run. The time it takes to get about half way down the trough should then be recorded.

This process will set a standard or an expected result for a perfect product. From this baseline, acceptable limits should be set by time. For example, a reading of 16 in 85 seconds might be the standard for a perfect product at 30° C. Acceptable variations can range from a reading of 16 in 81 seconds to a reading of 16 in 89 seconds. Again, the product temperature should be 30° C.

A similar procedure should be followed for each of your products tested with the Bostwick Consistometer. The standards thus should be recorded in a QC results chart and stored as reference for ISO or similar quality control inspections.

This table shows typical standards and acceptable limits for three hypothetical products:

	Marbleized A	Syrup C	Mission 5
Product Temperature	30°C	42° C	50°C
Distance Standard	16	17.5	15
Time Standard	85 Seconds	58 Seconds	42 Seconds
Allowable + Time	81 Seconds	62 Seconds	46 Seconds
Allowable - Time	89 Seconds	55 Seconds	40 Seconds

We have had frequent requests to develop a reference standard for ISO and other quality control inspections. In an attempt to meet these requests, CSC Scientific conducted extensive research to find a suitable material - a material with a consistent viscosity that would repeat results from test to test. The problem we had with seemingly promising materials was a high sensitivity to small temperature changes. After exhaustive experimentation, we concluded that the prevalent effect of temperature on Bostwick Consistometer results abrogated the practicality of a universal standard.

The critical issue in consistent and repeatable CSC Bostwick Consistometer operation is in the set-up. Leveling the trough is the principal requirement for getting repeatable results on a sample at a fixed temperature.

Establishing and recording Bostwick results on the perfect or quality control standard product is the only practical way to develop a calibration. This should be done with the user’s product at the testing site.

Sorry to have to carry this message. You have to do your own calibration for each of your products.

I hope this was helpful to you.

As always a perplexed,

Art

P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for e-mail notice by jotting your address in the box just to the right of the title.

Surface Tension – Tensiometer Update

This ramble is about changes in the Surface Tension Equipment landscape.

For decades it seems -- I guess it has been decades -- CSC Scientific (with the Precision and Interfacial Models) and Fisher Scientific (with the Tensiomat^©) have shared success in supplying the need for liquid surface tension tensiometers throughout the World.

Fisher has periodically evaluated discontinuing Tensiomat© manufacture. This year, the company decided to cease production. The CSC Scientific  models are recommended as replacements. Fisher Scientific can provide either of the CSC Scientific Tensiometers.

CSC has two Tensiometer models:

• Precision Tensiometer - Readings are obtained from an upward pull through the sample.

• Interfacial Tensiometer – Readings can be obtained from an upward pull or a downward push

The CSC Interfacial Tensiometer is needed when interfacial tension is calculated between a less-dense fluid and a heaver one located below the interface. The ring is rigidly attached to the measuring arm to obtain a downward measurement. The Interfacial Tensiometer is also recommended when the tested material is a thick liquid. This more easily facilitates setting up the ring below the liquid surface.

One important consideration in the tensiometer transition is the availability of duNouy Rings to replace damaged ones. Several Tensiomat© customers have successfully used CSC-manufactured rings. We believe that this will be the experience in most instances.

In order to further help with the transition, we will repair Tensiomat© brand Tensiometers and will do so as long as parts are available.

New replacement rings (part number: 70537000) can be ordered directly from our on-line store or by telephone at 800-621-4778. Of course, we can help you with a new unit. Also, we offer background and application information on our Tensiometer Models.

If you are a a user of CSC Tensiometers or are otherwise not affected by this discontinuation but have a colleague with a Tensiomat^©, perhaps you can forward this article, thus providing them with a source for answers to questions about repairs and replacements.

We hope this has been helpful to you or to one of your colleagues.

A still somewhat dazed,

Art

P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is click on the RSS Feed symbol at the upper left and you will get a notice when a new one is published. Or, if you prefer, you can also subscribe for e-mail notice by jotting your address in the box just to the right of the title.