154 The Philippine Journal of Science isie 



(by volume) of chemically pure hydrochloric acid to one part 

 of distilled water should be employed. Such a solution has 

 a density of approximately 1.098 at 15.5°C. and contains 19.53 

 per cent acid. The temperature of the acid should never be 

 higher than 45 °C. A 15-centimeter square (or larger piece) 

 of galvanized sheet is weighed, placed in the acid, and allowed 

 to remain until perceptible effervescence ceases, which should 

 require only two or three minutes. It is then removed and 

 washed. If any zinc still remains, the sheet is again placed in 

 the acid until this is dissolved, which usually requires only a 

 minute or two. It is removed, washed in water, then in alcohol, 

 placed in a drying oven for a few minutes, cooled in a desiccator, 

 and weighed. 



Preliminary tests convinced me several years ago that this 

 is a very satisfactory method, but at that time no detailed 

 investigation was undertaken. The fact that iron dissolves so 

 readily in hydrochloric acid under some conditions would, lead 

 one to think that the acid was not suitable for this purpose. 

 However, the present work shows that no iron (except, perhaps, 

 a trace) other than that alloyed with the zinc goes into solution, 

 provided the temperature and density of the acid are properly 

 controlled. 



COMPAEISON OP THE LEAD ACETATE AND HYDROCHLORIC ACID 



METHODS 



Preliminary experiments showed that in both methods some 

 iron was removed from the sample. In the lead acetate method 

 this iron comes entirely from the zinc-iron alloys, because the 

 basic lead acetate solution does not attack the iron base. A 

 number of tests were run to determine if the same thing was 

 true with the hydrochloric acid. Variations had been noticed 

 in results obtained by both methods, and it was desired to deter- 

 mine whether these were due to errors in the methods or to 

 lack of uniformity in the coating itself. Consequently, in every 

 case after the coating had been removed, the solution and all 

 wash waters used in the operation were placed in a flask, made 

 up to volume, and the iron and zinc were determined in an 

 aliquot portion. 



This operation was found to be much simpler in the hydro- 

 chloric acid than in the lead acetate solution. In the latter 

 case the first analyses were made by simply pipetting off the 

 solution from the metallic lead. This gave results which were 

 incorrect. Approximately 50 per cent of the zinc had been ab- 

 sorbed by the metallic lead. It was found necessary first to 



