Constitution of the Subsalts of Copper. 503 



bined water save one equivalent, but also, as all salts are 

 neutral salts, that water replaces sulphuric acid with the oxide 

 of copper, thus playing the part of an acid, or vice versa; the 

 first view is not borne out by experiment, and the second ex- 

 hibits either water or oxide of copper in a new and singular 

 point of view, as possessing both basic and acid characters; 

 in sulphate of water or sulphate of copper, a base; in the sub- 

 sulphates of copper, either the water or the oxide of copper, 

 an acid. Whether the true meaning has been attached to 

 the laws quoted as laid down by Mr. Graham, I am un- 

 able to say. If I have misunderstood his meaning, the mis- 

 statement has been unintentional, and is owing to having ac- 

 cepted these sentences for what they express, viz. that all 

 sulphates of the so-called magnesian class of oxides contain an 

 atom of constitutional water, and that all salts are neutral. 

 I presume, however, that the subsulphates of copper will be 

 added to the already somewhat long list of specified exceptions 

 to this latter law. In his ' Elements of Chemistry,' p. 169, Mr. 

 Graham, speaking of subsalts, says, " The compounds of 

 the present class appear to be salts which have assumed a 

 fixed metallic oxide in place of this water," that of crystalli- 

 zation, " they may therefore be truly neutral in composition, 

 the excess of oxide not standing in relation of base to the 

 acid." And this passage surely bears out the meaning I have 

 attached to the former expressions, and is wholly incompati- 

 ble with the observed facts relative to the subsulphates of 

 copper; for under this view there should be but one, viz. 

 SO s HO + 5CuO, corresponding with the crystallized blue 

 sulphate of copper, a compound at present not known to 

 exist. 



I now come to Dr. Kane's views on this point. In the 

 paper already referred to, he likewise assumes as a " general 

 principle that the transition from the neutral to the basic con- 

 dition in salts takes place by the replacement of water by me- 

 tallic oxide, has, as I conceive, received the fullest confirma- 

 tion." This is clear and distinct, but I submit that this " ge- 

 neral principle" is overthrown by what we have seen to be 

 the constitution of the various subsulphates of copper. Fur- 

 ther on it is stated, that " a. great number of circumstances 

 conspire to render the derivation of the basic sulphates of the 

 magnesian class, from the neutral condition, exceedingly 

 complicated. Thus the neutral salts crystallize with quantities 

 of water variable within very extensive limits, and the pro- 

 portion of metallic oxide by which it may be replaced is sub- 

 ject to variations equally wide : moreover, the replacement of 

 the water by metallic oxide may be but partial, and hence the 



