104 DEPARTMENT BULLETIN 12 16, TJ. S. DEPT. OF AGRICULTURE 
In this formula the total area — that is, both sides of the sheet — is measured. 
To place this on the ordinary sheet basis, as expressed on zinc-coated sheet, 
rhe above figure should be doubled. For very light coatings (about 1 ounce per 
square foot) loo cubic centimeters of acid are sufficient. With coatings of 2% 
ounces per square foot or heavier 300 cubic centimeters of acid should be used. 
To standardize the equipment five or six zinc-coated specimens of any con- 
venient gauge or size are weighed, the rise in temperature determined for the 
apparatus, thermometer, and volume of acid. The samples are washed, dried, 
and reweighed and the difference in weight noted. The weight loss in grams 
is divided by the corresponding rise in temperature in degrees. When care- 
fully determined the average of the above five or six determinations will give 
:i conversion factor which is reliable for the equipment used and for the volume 
of acid employed. Factors may be determined for any volume of acid in like 
manner. 
EVOLUTION OF HYDROGEN METHOD 
This method consists in measuring the hydrogen evolved from the action of 
hydrochloric acid containing antimony chloride upon a definite area of gal- 
vanized surface. By this method it is not required to cut any portion of the 
article to be tested, as with the Cushman coating tester, a 2%-inch ring is 
sealed to a portion of the surface. Acid is then added, which attacks the 
coating within the area of the ring, and the evolved hydrogen is measured by 
a suitable gas burette. After removal of the spent acid the stripped spot is 
washed, dried, and may either be painted or coated with a suitable metallic 
coating. The article is, therefore, not mutilated. A full description of the test 
is found in the 1920 Proceedings of the American Society for Testing 
Materials (8). 
The results obtained by this method check very closely with those obtained 
by the regular hydrochloric acid — antimony chloride method. The main objec- 
tion to this method is the fact that the coating upon only one side of a sheet 
is obtained, and as the coating upon galvanized sheets is not always exactly 
the same on each side doubling the figures obtained on one side of the sheet 
will not always give the real amount of coating on both sides of the sheet. 
This tester finds use, however, when it is necessary to test sheets or culverts 
already installed and where it is desired that the articles shall not be mutilated, 
as would be necessary in taking a regular sample. 
66. METHOD OF TEST FOR UNIFORMITY OF GALVANIZING 
OR SPELTER COATING ON WIRE 
1. This method gives in detail the test to be applied to galvanized wire. 
2. Coating. — The galvanizing shall consist of a continuous coating of pure 
zinc of uniform thickness, and so applied that it adheres firmly to the surface 
of the iron or steel. The finished product shall be smooth. 
3. Cleaning. — The sample shall be cleaned before testing, first with carbon 
tetrachloride, benzine, or turpentine, and cotton waste (not with a brush), 
and then thoroughly rinsed in clean water and wiped dry with clean cotton 
waste. 
4. The samples shall be clean and dry before each immersion in the solution. 
5. Solution. — The standard solution of copper sulphate shall consist of com- 
mercial copper sulphate crystals dissolved in cold water, about in the proportion 
of 36 parts, by weight, of crystals in 100 parts, by weight, of water. The solu- 
tion shall be neutralized by the addition of an excess of chemically pure cupric 
oxide (CuO). The presence of an excess of cupric oxide will be shown by the 
sediment of this reagent at the bottom of the containing vessel. 
6. The neutralized solution shall be filtered before using by passing through 
filter paper. The filtered solution shall have a specific gravity of 1.186 at 65° F. 
(reading the scale at the level of the solution) at the beginning of each test 
In case the filtered solution is high in specific gravity, clean water shall be 
added to reduce the specific gravity to 1.186 at 65° F. In case the filtered 
solution is low in specific gravity, filtered solution of a higher specific gravity 
shall be added to make the specific gravity 1.186 at 65° F. 
7. As soon as the stronger solution is taken from the vessel containing the 
unfiltered neutralized stock solution, additional crystals and water must be 
added to the stock solution. An excess of cupric oxide shall always be kept 
in the unfiltered stock solution. 
