April, 1923
I S D C S T R T I L A S D ESGISEERISG CHEXISTRY
“10 cc.” If the concentration of sulfate is low, a 20-cc. sample of boiler water may be taken and treated as indicated for the 10-cc. sample. I n this case the scale marked “20 cc.” is used to indicate the sulfate concentration. With this type of apparatus an inexperienced obserrer can duplicate results to 200 p. p. ni., which is all the accuracy that can be desired for the determination. Of course, a sulfur photometer as described by Parr,6 or the Jackson turbidimeter could be adapted to this determination, but the degree of accuracy required is not sufficient to justify such exactness. ”Fuel, Gas, IVater and Lubricants,” 1922,p 174
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Application of Analytical Data
There are two methods of maintaining the carbonate and sulfate concentrations in the correct ratio. The first is to adjust the inflow of soda ash solution so that the carbonate concentration in the boiler water will be in the proper ratio t o the sulfate as determined. The second is to maintain a fixed satisfactory sulfate concentration by blow-down, and hence a uniform carbonate concentration. Reference to a curve based on the solubility product ratio for the pressure of operation, in either case will give information as to the proper concentrations to maintain.
Laboratory Tests on Finishes’ By H. C. Mougey GENERAL A l O T O R S RESEARCH C O R P . , DAYTON, OHIO
HE testing of an automobile finish in the laboratory 116 days. The short life of the varnish with the 180 kauri rewith the view of predicting the life of the finish in ser- duction is due to the poor undercoat of the rubbing varnish vice is a very difficult matter. The writer is in hearty failing and taking the finishing varnish with it. I n other sympathy with attempts to establish such tests, but a t the words, a finishing varnish will not give its full life unless expresent time he feels that, in addition to laboratory tests of the posed over proper undercoats, and if exposed over undermaterials used in the seDarate coats, all new automobile coats such as are ordinarilly used in automobile finishing, a long oil finishing varnish finishes should be tested c y may give poor results as exposing them on test racks Laboratory tests on finishing materials cannot be dicompared with a short oil, under standard exposure rectly interpreted into terms of service unless the entire harder drying finishing varconditions, supplemented system of coats is studied as a whole. This requires a nish. with practical tests such as consideration of the properties of each coat, the relation Pulsifer3 recognizes the actual service on cars. of the coats to each other, the methods of application necessity of proper coats There are several reasons and drying time, and the service expected of the finish. directly beneath the finishwhy laboratory tests do not So-called accelerated tests are really identification tests ing varnish, and this is the always give results that in most cases. Instead of subjecting the material to be are proportional to service fundamental fact behind tested to a series of forces tending to destroy the material tests. Pulsifer2 has called the system, recommended and having both these forces and the power of resistance by him, of increasing elasattention to the fact that of the sample changing in exactly the same manner as the tests on finishing varticity of the individual they would in actual service, the tests, as usually connishes should not be concoats as the finishing varducted, simply show the way in which the sample reacts sidered alone, but that such nish coat is approached. to the particular test. factors as elasticity, moisUnless this method is folture resistance, and film lowed there is no definite must all be considered toconnection between laboragether in estimating service durability. This estimate is tory tests and actual service, and unfortunately it frenecessarily based on the assumption that other factors are quently happens that this method is not followed. On favorable for best results, but it frequently happens that account of these facts, the entire system of undercoats and topcoats, dried as they would be in production, must be they are unfavorable. For example, Figure 1 shows the appearance of two finish- tested as a unit to determine the life of the finish. ing varnishes of very different average durabilities, after DRYING 4.5 months’ exposure. One of these varnishes ( A ) has kauri reduction of 180 and under proper conditions is very Another factor affecting durability is the thoroughness of durable. The other ( B ) has a kauri reduction of 40, but drying regardless of the undercoats used. As an illustration even under favorable conditions it never shows a high dura- of this, a black color varnish made by grinding black pigbility. In this particular case both finishing varnishes are ment in a long-oil, ester-gum, wood-oil varnish was exposed applied over the same undercoat on different sections of the over bare steel. On the first panel, the varnish was airsame test panel. The rubbing varnish (C) under these fin- dried 2 days, on the second panel it was baked 2.5 hours a t ishing Yarnishes is of the kind ordinarily used in automobile 135” C., and on the third panel it was baked 1 hour a t 204.5’ finishing, and unprotected with finishing varnish it has a C. The life of these panels was, respectively, 3 . 5 , 9, and 12 very short life on outdoor exposure. In this particular months. In a similar manner, if two varnishes of the same test the unprotected rubbing varnish failed in 47 days, t,he kauri reduction are exposed over suitable undercoats, the finishing varnish with a kauri reduction of 40 failed in 123 one that dries better will usually be more durable, and this days, and the varnish with a kauri reduction of 180 failed in difference in drying may overcome a very great difference in the kauri test. For example, a certain hard-drying Presented as discussion a t t h e symposium on “ T h e Physical Testing finishing varnish having a kauri reduction of 120 is on the of Varnishes” before the Section of Paint a n d Varnish Chemistry a t the 67th Meeting of the American Chemical Society, Washington, D. C . , April 21 t o average slightly more durable than another slower drying
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26. 1924. 2
J . S o < . .1ulomoiise Eng., 10, 12 (1922).
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J. SOC.Auromofioe Eng, 12, 89 (1923).
kiwi ri!ilu?th of IXf). wliim hot,Ii v n r n i d m iirc eqiuscd uiidcr siinihr cotiditioiia wit11 suitaik uiidercoat.s. lri aotiml service a varnish may fail on awouiit of a l m s i o n or si:rai.clring. 11, general, a liard-drying vinmislr will resist tho scrati~liingto a greater degree than oiie which docs iiot dry so hard. This is ~ c lknown, l and firiisliirig variiishi:s designed fur iise on whecls itro harrlcr dryiiig than those ~lo+ignedfor liiiikiiiiig
varzsiA wliicla
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Figure l~--Txo Finishing varnishes affer 4.5 Monrhs’,&aposure
oii autoniohilc liodies, Init if both were exposed on k a t panels under proper conditions. the body finishing would outwear ilrat intended for wheels, and uTould certainly he graded IiiEher ., hv a lnborat,orv test tlran i?.ould t.tie wheel finishing varnish. All these illustrations indicate tliat. in addition to laboratory tests, it is iiecessary to consider such factors as the surfaces upoii which the materials are applied, methods of RPplication, and the service required of the finish. If these and additional factors are known anti proper allowances are made for them, it may be possible to make a scientific guess as to the relative durability of two fiiiishes of the same type. This is especially true if we have enough data shoming the relatioii of the laboratory tests to the durability of the finish in serviix. IIowever, if 5i.e ham a new type of finislr, these relationships may ILO longer iipply. For example, a standard test of black baking fender eiiamel is to heiid the test panel 180 degrees on itself. Vit,reons enamel or window glass will not stand such a test, hut both vitreous enamel and window glass are very much more resistant to exposure than is black baking fender enamel. During tbe past few years the ultra-violet light has been used vcry much in so-called accelerated testing of finishes. Although it is possible to secure failure of finishes by this method, the writer has not been ahle to find a direct relationship between ultra-violet light tests and service tests when different types of materials are comparcd, and variations in the application of the ultra-violet light tests make such groat differencesthat it is very difficult t,o make predictions RS to the service durahility of two finishes, eiwi though they are of the same type. For example, the lint method used to test fiiiishes by the ultra-violet light was simply to expose the test panels undrr the light. The first tests were on black baking fender enimel, arid much to everyone‘s surprise tlie panels failed on the test racks on t,lir roof hefore they did under the ultra-violet light.
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I iie p m i ~ l s~iwi:tlicrI sr,tikcd in water overnight aid espvsed to tlie ultra-vinlct light during the day. This gave iailores in a very few days, but unless care was ta.ken t o dry the panels of surface water the results vere of no value, failure occurring in a few minutes at the area,s where surface water lay on the panels. Finishing varnishes subjected to this test usually failed in. one cycle, wit.h no relation hetween this test and the durability of the varnish. It w~ apparent that this test favored bard-drying finishes, and the test, was t.lreri modified to use the robtirig wheel, :is shown in Figure 2 . The paiirls were mounted on the rim of the dieel, and t.lie wheel, half immersed in water, wasrot,ntcd under the ultra-violet light at. tlic rate of two revolutions per boor, tlnis soaking the finish, allowingtime for draina.geand evaporation of the surface moisture, and t,heir expsirig the panel t,m the light. Duco, wliicli nrould withstand exposure on the roof test mcks o x r 2 years, would fail i n 2 days, while a finishing varnish Iiaving a life of 3 months on the roof test would stand 2 or 3 weeks under this test. Appnrcntl connection hetween the test and the life of fini on tlie roof test racks. Tlie next method that was tried, and the one now in use. involves continuous day and night rotation of the w l i d vith the light turned on only during the day. This bits given much better results. but since it has been operating Iiut a short time, no definite report upon it can be made at tlii? time. So-called accelerated tests are really identification tests in most cases. Instead of subjecting the material to he tested to a series of forces tending to destroy the material and having both these forces and the power of resistanceof the sample changing in exactly the same manner as they would i ~ i actual service, the tests, as usually conducted, simply sliow the way in which the sample reacts to the particular test. If previous records have shown that a certain kind of inatcrial which reacts to several empirical tests in a certain manner is suitable for t.he use &ended, another sample of the s a n e
type wbicli gives similar results to the einpirieal tests, should also he suitnhle, under the same conditions. However, another material of a different type, which fails to meet these tests, may or may not give better results in actual service, anti identification tests cannot accurately predict the resilltn that, will be sewred.
