April, 1923 I S D C S T R T I L A S D ESGISEERISG CHEXISTRY 41 1

“10 cc.” If the concentration of sulfate is low, a 20-cc. sam- ple of boiler water may be taken and treated as indicated for the 10-cc. sample. In 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 re- quired is not sufficient to justify such exactness.

”Fuel, Gas, IVater and Lubricants,” 1922, p 174

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 CORP. , DAYTON, OHIO

HE testing of an automobile finish in the laboratory with the view of predicting the life of the finish in ser- vice is a very difficult matter. The writer is in hearty

sympathy with attempts to establish such tests, but a t the present time he feels that, in addition to laboratory tests of the materials used in the seDarate coats, all new automobile

116 days. The short life of the varnish with the 180 kauri re- duction is due to the poor undercoat of the rubbing varnish failing and taking the finishing varnish with it. In other words, a finishing varnish will not give its full life unless ex- posed over proper undercoats, and if exposed over under- coats such as are ordinarilly used in automobile finishing, a

T finishes should be tested c y exposing them on test racks under standard exposure conditions, supplemented with practical tests such as actual service on cars.

There are several reasons why laboratory tests do not always give results that are proportional to service tests. Pulsifer2 has called attention to the fact that the tests on finishing var- nishes should not be con- sidered alone, but that such factors as elasticity, mois- ture resistance, and film must all be considered to-

Laboratory tests on finishing materials cannot be di- rectly interpreted into terms of service unless the entire system of coats is studied as a whole. This requires a consideration of the properties of each coat, the relation of the coats to each other, the methods of application and drying time, and the service expected of the finish.

So-called accelerated tests are really identification tests in most cases. Instead of subjecting the material to be tested to a series of forces tending to destroy the material and having both these forces and the power of resistance of the sample changing in exactly the same manner as they would in actual service, the tests, as usually con- ducted, simply show the way in which the sample reacts to the particular test.

gether in estimating service durability. This estimate is necessarily based on the assumption that other factors are favorable for best results, but it frequently happens that they are unfavorable.

For example, Figure 1 shows the appearance of two finish- ing varnishes of very different average durabilities, after 4.5 months’ exposure. One of these varnishes ( A ) has kauri reduction of 180 and under proper conditions is very durable. The other ( B ) has a kauri reduction of 40, but even under favorable conditions it never shows a high dura- bility. In this particular case both finishing varnishes are applied over the same undercoat on different sections of the same test panel. The rubbing varnish (C) under these fin- ishing Yarnishes is of the kind ordinarily used in automobile finishing, and unprotected with finishing varnish it has a very short life on outdoor exposure. In this particular test the unprotected rubbing varnish failed in 47 days, t,he finishing varnish with a kauri reduction of 40 failed in 123 days, and the varnish with a kauri reduction of 180 failed in

Presented as discussion a t the symposium on “The Physical Testing of Varnishes” before the Section of Paint and Varnish Chemistry a t the 67th Meeting of the American Chemical Society, Washington, D. C . , April 21 to 26. 1924.

2 J . So<. .1ulomoiise Eng. , 10, 12 (1922).

long oil finishing varnish may give poor results as compared with a short oil, harder drying finishing var- nish.

Pulsifer3 recognizes the necessity of proper coats directly beneath the finish- ing varnish, and this is the fundamental fact behind the system, recommended by him, of increasing elas- ticity of the individual coats as the finishing var- nish coat is approached. Unless this method is fol- lowed there is no definite connection between labora-

tory tests and actual service, and unfortunately it fre- quently happens that this method is not followed. On account of these facts, the entire system of undercoats and topcoats, dried as they would be in production, must be tested as a unit to determine the life of the finish.

DRYING Another factor affecting durability is the thoroughness of

drying regardless of the undercoats used. As an illustration of this, a black color varnish made by grinding black pig- ment in a long-oil, ester-gum, wood-oil varnish was exposed over bare steel. On the first panel, the varnish was air- dried 2 days, on the second panel it was baked 2.5 hours a t 135” C., and on the third panel it was baked 1 hour a t 204.5’ C. The life of these panels was, respectively, 3.5, 9, and 12 months. In a similar manner, if two varnishes of the same kauri reduction are exposed over suitable undercoats, the one that dries better will usually be more durable, and this difference in drying may overcome a very great difference in the kauri test. For example, a certain hard-drying finishing varnish having a kauri reduction of 120 is on the average slightly more durable than another slower drying

a J. SOC. Auromofioe Eng, 12, 89 (1923).

liiiikiiiiig varzsiA wliicla 1i:ir 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 almsion or si:rai.clring. 11, general, a liard-drying vinmislr will resist tho scrati~liing to a greater degree than oiie which docs iiot dry so hard. This is ~ c l l known, and firiisliirig variiishi:s designed fur iise on whecls itro harrlcr dryiiig than those ~lo+igned for

Figure l~--Txo Finishing varnishes affer 4.5 Monrhs’,&aposure

use 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 labo- ratory tests, it is iiecessary to consider such factors as the sur- faces upoii which the materials are applied, methods of RP- plication, 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 fin- ish 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 relation- ship 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 differences that 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 l int 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.

, > I iie p m i ~ l s ~iwi: tl icrI sr,tikcd in water overnight aid es- pvsed 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 sur- face water lay on the panels. Finishing varnishes subjected to this test usually failed in. one cycle, wit.h no relation he- tween 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, allowing time for draina.ge and evapora- tion 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 hav- ing 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.