THE PREPARATION OF PURE MATERIALS. 75 



dried as much as possible in the centrifugal machine, and the drying was 

 completed in an air-bath at 110. These operations were carried out as 

 much as possible under the protection of a very large inverted funnel, and 

 the dish was kept covered with a large watch glass, to avoid the introduc- 

 tion of dust. This sample was called A and was used in the preliminary 

 series and in experiments -1 and 5 of the final series of quantitative experi- 

 ments. 



Sample A was dissolved in concentrated sulphuric acid, boiled, crystal- 

 lized as acid sulphate by cooling, centrifugally drained, converted into 

 the normal sulphate by adding water, washed, and dried as before. This 

 sample was called sample B. Since the mean of the results with this sam- 

 ple is the same as the mean of experiments 4 and 5, in which sample A 

 was used, it is evident that the boiling of the sulphuric acid solution fol- 

 lowed by a crystallization in two different crystalline forms did not affect 

 the result ; therefore further purification seemed unnecessary. 



HYDROCHLORIC ACID. 



Hydrochloric acid, which was only used as a gas, was made from two 

 sources. In experiments 5 and 6 the hydrochloric acid was made by drop- 

 ping pure sulphuric acid on pure ammonium chloride. In the other ex- 

 periments the best commercial concentrated hydrochloric acid was used. 

 Richards and Wells 1 have shown that this acid contained no other halogen 

 or arsenic ; it was therefore suitable for our purpose. 



THE FUSION OF ARGENTIC SULPHATE. 



Much thought was expended on the devising of a piece of apparatus 

 which should be suitable not only for the fusion of argentic sulphate, but 

 also for the quantitative conversion of the sulphate into the chloride. 

 Finally the simple symmetrical tube shown in the diagram was found to be 



\1 



Fig. 3. Quartz tube used to contain the argentic falls. One-half actual size. 



best. It was the outcome of several trials and suggestions, and consisted 

 of a thin cylindrical tube of fused quartz with smaller quartz tubes fused 

 upon the ends. 1 The tube was very light, weighing less than 6 grams. A 

 very fine platinum wire was wrapped many times around the constricted 



Richards and Wells, loc. cit. 



2 We are greatly indebted to Professor Baxter for his kindness in making this 

 apparatus from a fine quartz tube and a quartz test-tube. To Mr. F. B. Coffin also 

 we are indebted for a suggestion which led to a modification of the original shape 

 of the tube. 



