238 M. Carey Lea — Properties of Allotropic Silver. 



moist state on a filter, or be placed in a pasty condition in a 

 corked vial and so kept moist for months, without alteration. 



The gold-colored form on the contrary, tends constantly to 

 revert to ordinary silver. This is especially the case whilst it 

 is moist, so that from the time of its formation, it must be 

 separated from its mother water and washed as rapidly as 

 possible, otherwise it loses its brilliancy and purity of color 

 and changes to a dark dull gray form of normal silver. On 

 the filter, its proper color is pure black with a sort of yellow 

 shimmer (the gold color appearing as it dries) often, especially 

 if allowed to become uncovered by the water during washing, 

 it will change superficially to gray.* But if the washing is 

 done rapidly with the aid of a filter pump and a pressure of 

 four or five inches of mercury, the allotropic silver obtained, 

 when allowed to dry in lumps, or brushed over paper or glass, 

 is at least equal to pure gold in color and in brilliancy. With 

 the blue product such precautions are wholly superfluous. 



Of the facility with which the gold colored form is con- 

 verted into normal silver, I have recently had a somewhat 

 singular proof. I brought with me to my summer home a 

 number of specimens in tubes, some recently prepared, some 

 dating back as far as two and a half years, together with other 

 tubes containing specimens of white silver spontaneously formed 

 from the gold colored. On opening the box no tubes of gold 

 colored silver were to be found, all had changed to white. 

 But the same box contained pieces of paper and of glass on 

 which the same material had been extended ; these were 

 wholly unchanged and had preserved the gold color perfectly. 

 Apparently the explanation was this, the mere vibration caused 

 by the jarring of a journey of 600 miles by rail and steam- 

 boat had had no effect in changing the molecular form, but 

 the material contained in the partly filled tubes had been also 

 subjected to friction of pieces moved over each other, and 

 this had caused the change. To verify this explanation I 

 prepared fresh material, filled three similar tubes each one 

 quarter full, but in one forced in cotton wool very tightly to 

 prevent frictional motion. These tubes were packed in a 

 small box and sent over 2400 miles of railway. The tubes 

 with loose material came back much altered, one was nearly 

 white, and as the change has been set up will probably in a few 

 days be entirely so,f another with loose material was also 

 changed but not as much as the first mentioned. The tube 

 filled up with cotton came back unaltered. So that continued 

 friction of pieces sliding over each other will cause a change 

 to take place in a few days which otherwise might have 



* When well washed, this form can also be preserved for a time in the moist 

 condition in a corked vial, as I have lately found, 

 •j- Has since become so. 



