on Allotropie Silver. 341 



hydrochloric acid, we shall obtain a dark chestnut-brown or 

 sometimes purple-brown substance, which on examination 

 proves to be a mixture of silver subchloride and protochloride. 

 When, after complete removal of the excess of hydrochloric 

 acid by thorough washing or, better, by boiling with distilled 

 water, the substance is treated with cold dilute nitric acid, 

 that portion of the subchloride which is not combined with 

 the normal chloride is broken up, and there remains proto- 

 chloride of a very rich and intense rose-colour*. 



The production of silver subchloride in all these cases would 

 seem to indicate that the reduction when the acid was added 

 was incomplete ; and that in case (1) a subsalt, and in cases 

 (2) and (3) a suboxide was first formed as an intermediate 

 step before complete reduction. Either of these substances 

 would of course give rise to the formation of subchloride when 

 treated with hydrochloric acid. It is important to observe 

 that this result is to be obtained only by interrupting the 

 reaction before it is complete. When, for example, allotropie 

 silver in solution is produced by the action of sodic hydroxide 

 and dextrine, and after complete reduction hydrochloric acid 

 is added, the liquid becomes filled with grey normal silver 

 which presently collects to a cake. When this cake is well 

 washed and boiled with water and then treated with dilute 

 nitric acid, solution takes place : a trace of protochloride is 

 left behind. It has been mentioned elsewhere that hydro- 

 chloric acid, though without action on ordinary silver, is 

 capable of forming a variable quantity of protochloride when 

 placed in contact with allotropie silver. 



I have not met with any exception to this general principle, 

 that when a reaction leading to the formation of allotropie 

 silver is interrupted by the addition of hydrochloric acid, 

 subchloride is abundantly formed as one of the products. 



In all such cases the reduction is evidently indirect. The 

 silver does not lose at once the whole of its oxygen, but appa- 

 rently passes through an intermediate form, probably Ag 4 0, 

 the reduction of which tends to the formation of allotropie 

 silver. 



These facts lead directly up to the question, Does silver 

 exist in its subsalts in the allotropie form ? There are some 

 facts that would support this view, especially the very rich 

 and varied coloration of the subsalts corresponding to the 



* This is a very "beautiful reaction and deserves more particular mention 

 than can be given here. It is perhaps the best means for obtaining silver 

 protochloride, for which purpose I have often employed it, both on 

 account of its facility and certainty, and the very beautiful colour of the 

 product. 



