158 The Philippine Journal of Science 1916 



such a high temperature, it is recommended that the solution 

 be kept at 45° or below." 



CRITICISM OF AN ANALYTICAL METHOD SOMETIMES USED 



Some chemists use an analytical method for determining the 

 zinc, which is as follows: 



A 30-centimeter square of the original material is weighed, 

 and the weight is recorded. A few small pieces are then cut 

 and weighed on an analytical balance, and the percentage of zinc 

 is determined by analysis. The weight of the large square in 

 grams is then multiplied by this factor to give grams of zinc 

 in that area. Such a procedure is, of course, erroneous. The 

 present work has shown that the galvanizing on one sheet 60 

 by 75 centimeters may vary as much as 8.76 grams per 900 

 square centimeters (fig. 1). 



A SIMPLE AND RAPID METHOD FOR DETERMINING IRON 



Any solution which will remove all the zinc from a piece of 

 galvanized iron will also remove the iron in the zinc-iron alloy. 

 If the zinc is then calculated from the loss in weight, there will 

 be an error due to the iron that has been dissolved. This error 

 is comparatively so small that it is usually disregarded. How- 

 ever, it is sometimes desired to correct it, and this may be 

 accurately done by precipitating the iron with ammonia and 

 weighing as the oxide. 



The iron may be determined approximately by a much simpler 

 procedure. The results are not so accurate, but are sufficiently 

 so for most purposes. While the coating is being dissolved by 

 the acid, the iron in solution is being reduced by the nascent 

 hydrogen, and the rise in temperature aids the reaction. The 

 tray in which the test is made should be nearly covered, with 

 only a small outlet for the evolved gases. The minimum volume 

 of acid should be used — about 350 cubic centimeters. As soon 



" In practice it is not necessary to use a separate portion of hydrochloric 

 acid for each sample. In using any method for the first time, or in testing a 

 brand of galvanized iron with which he is unfamiliar, it is well for a chemist 

 to determine the alloyed iron and the loss in weight of the stripped sheet 

 in the testing solution. For routine tests the hydrochloric acid is placed 

 in a jar or crock which is large enough to accommodate one or more pieces 

 of the galvanized iron (without touching each other). This same acid may 

 be used for a number of samples until the action becomes too slow on account 

 of the low concentration of hydrogen ions. The only necessary precaution is 

 to observe the temperature from time to time and not allow it to exceed 45 °C. 



