PREPARATION OF PURE MATERIALS. 49 



the silver thus prepared gave the same combining weight as that cooled 

 under a full atmosphere's pressure of hydrogen. Thus the conclusion of 

 Richards and Wells and of Baxter that silver can not dissolve a weighable 

 amount of hydrogen was confirmed. 



The buttons thus obtained were etched to remove lime, and if too large 

 to go into the flasks used for the synthesis, were cut with a cold chisel or 

 a jeweler's saw, observing all the precautions recommended by Richards 

 and Wells. The fragments freed from superficial iron were washed and 

 dried, sometimes in the electric oven in air at 150 for an hour, sometimes 

 in a vacuum at dull redness, and sometimes in a reduced pressure of hydro- 

 gen. Judging from the constant combining weight, all these methods 

 were equally good. 



Water. The water was distilled first with alkaline permanganate 

 through a glass condenser, and then, after the addition of a small drop 

 of dilute sulphuric acid, through a carefully cleaned condenser of block 

 tin. Needless to say, dust was excluded as much as possible, and distilla- 

 tions were conducted immediately before the water was needed, in order 

 to avoid absorption of gases or solution of solid matter. 



Air. It will be remembered that Stas allowed his solutions of argentic 

 nitrate to evaporate very slowly, the vapors diffusing out through the neck 

 of his flask and condensing in a suitable receptacle. Under these condi- 

 tions the evaporation required seventy-two hours of continuous heating 

 an unnecessarily prolix process. To hasten the escape of aqueous vapor, 

 it was resolved to maintain a gentle current of pure dry air throughout the 

 process. The air for this purpose was delivered from a water pump,. 

 which must have removed some of the original impurities. It was passed 

 first through a tall Emmerling tower filled with beads moistened with 

 concentrated sulphuric acid, to which a trace of potassic bichromate had 

 been added, and then through two more towers filled with a concentrated 

 solution of pure potash, being thus freed from ammonia and from acid 

 gases. Next it was passed through a tall drying tower of stick potash, to 

 a hard glass tube containing platinized asbestos heated to dull redness by 

 a Bunsen burner. The hot platinum was intended to destroy organic 

 matter. Hence it passed into a trap designed to catch asbestos shreds, 

 and finally, the air was dried by two towers of broken potash. The whole 

 purifying train was put together without rubber, all the pieces being 

 blown together except the hard glass tube, which was connected with the 

 soft glass on either side with joints so well ground that no lubricant was 

 necessary. The towers were glass-stoppered. Air thus purified and dried 

 contains nothing to injure the silver nitrate except possibly a minute 

 trace of ammonia, which might have come out of the potash solutions. 



