METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 103 
APPENDIX 
FIELD TESTS FOR DETERMINATION OF ZINC-COATED ARTICLES 
PREECE OR COPPER- SUP HATE DIP TEST 
The samples for the Preece test may be of any size, but should be free from 
as much cut surface as possible and should be carefully cleaned before starting 
the test. The samples are then dipped into not less than 100 cubic centimeters 
of copper-sulphate solution maintained at a temperature of 18° C. The samples 
are allowed to remain exactly one minute in the solution. They are then 
washed in running water and the copper deposit lightly rubbed off. Successive 
immersions of one minute each are continued, with the washing and cleaning 
of the sample between each one until the appearance of bright adherent copper 
indicates that the iron beneath the coating has been exposed. Should a small 
amount of copper be coated adherently to the zinc coating it must not be mis- 
taken for the end point in which the copper plates out onto the iron. The ap- 
pearance of copper within 1 inch of a cut surface is likewise not considered to be 
the end point of the test. 
The copper-sulphate solution is prepared by dissolving 36 parts of commercial 
copper sulphate crystals in 100 parts of water, then adding enough cupric oxide 
to neutralize any free acid. The solution is filtered or allowed to settle and 
decanted, then diluted with water until its specific gravity is 1.186 at 18°* C. 
It should always be used at this temperature. 
When material is tested by the Preece or copper-sulphate method the number 
of one-minute immersions which the sample shall withstand is specified. 
The amount of coating removed by a one-minute immersion in the copper- 
sulphate solution is, roughly, between 0.20 and 0.25 ounce per square foot of 
actual surface, or double this per square foot of sheets. 
This test is not as accurate in determining the average weight of coating upon 
a sample as is the hydrochloric acid-antimony chloride method, but is useful, 
however, in determining which are the thinnest portions of the coating. 
THERMAL METHOD * 7 
This method makes possible the determination of the zinc coating on iron 
and steel sheets and other articles without necessitating the use of an analytical 
balance. An accurately measured galvanized sample is immersed in a meas- 
ured amount of acid, the maximum temperature rise being recorded. Each 
0.1° rise in temperature is equivalent to a definite weight of zinc. 
The apparatus necessary for conducting this test is as follows: 
1. Testing jar. about 2 1 /> inches in inside diameter, with a capacity of about 
400 cubic centimeters flaring at the top if possible. 
2. Thermometer graduated in 0.1° C, with a range of about 50° C. 
3. Three hundred cubic centimeter graduated cylinder. 
4. Glass-stoppered bottle containing concentrated hydrochloric acid (specific 
gravity approximately 1.19). 
5. Rule for measuring : The sample is cleaned with gasoline, dried, and accu- 
rately measured. For testing zinc-coated sheet the usual 2*4 by 2% inch (or 
of equivalent area) specimen may be used, and for wire suitable lengths may 
be used as given in Table 8. 
A measured amount of hydrochloric acid (usually 200 cubic centimeters) is 
poured into the testing jar. The temperature of the acid is recorded after 
stirring and the sample is immersed in the acid, care being taken that the acid 
does not overflow the jar. During this time, and until the coating has been 
stripped from the piece, the temperature is watched until the highest point is 
reached and the temperature starts to decline. The rise in temperature is then 
recorded, and from a table of factors prepared for various quantities of acid 
the amount of zinc may be calculated. From the number of grams of zinc 
and the area of the piece in square inches the weight of coating may be cal- 
culated, as follows : 
Coating, ounces per square foot, _ Weight of zinc 5.08 square inches. 
actual surface in grams X Area, square inches. 
47 Described in papt'r by D. M. Strickland (15). 
