858 PROCEEDINGS OF THE AMERICAN ACADEMY 



striking when the perfect crystalline structure of the body is consid- 

 ered. I have observed a similar abnormal composition in the salt of 

 chloride of strontian, while the salt of chloride of potassium, for exam- 

 ple, even when crystallized in the most confused manner, has a compo- 

 sition agreeing completely with theory. 



Reserving further discussion for another occasion, when the subject 

 shall have been more thoroughly investigated, the following is the view 

 which I am at present inclined to take of this, as well as of some other 

 cases of >sirailar nature. 



The body in question may be regarded as composed of norynal salt, 

 of definite atomic constitution, to which is added a certain excess, varia- 

 ble in amount, of cyanide of mercury ; which latter is not combined 

 chemically icith the nominal salt, but enclosed like a foreign body in the 

 interstices of its crystalline structure. If this view be correct, the water 

 and barium should be present in the abnormal in the same relative pro- 

 portion in which they exist in the normal salt ; and if the excess of cy- 

 anide of mercury be deducted from the total salt analyzed, the barium 

 found should be in the same proportion in the residue as it is in the 

 normal salt. The one of which conditions is virtually included in the 

 other. 



The abnormal crystals of this salt, which I have examined, agree 

 pretty well with these conditions. Omitting details for the present, it 

 may be stated that the water thus calculated on the barium found is in 

 general deficient by about 0.5 per cent ; it agreed in one case very nearly 

 with the theory, and was found once to be 0.7 per cent in excess. In 

 this case unusual and perhaps inadmissible means had been taken to 

 remove adhering moisture. The salt is permanent in a not too dry 

 air, but in the air of a heated room, or in air kept dry by means of 

 sulphuric acid, it effloresces and loses at last nearly the whole of its 

 water of crystallization. When it is considered that the only means 

 we possess of drying such a salt without expelling the water essential 

 to its crystalline constitution is the mechanical operation of pressure 

 between paper, the above-mentioned deviation from theory, amounting 

 to 6 or 7 milligrammes on the quantity taken for analysis, may not be 

 thought to exceed the limits of the unavoidable errors of observation. 



Should this view be borne out by further investigation, and should it 

 be admitted that crystallized bodies may hold certain of their constitu- 

 ents, or even foreign substances, in a state not of chemical but of physical 

 or crystallographic combination, this property would serve to explain the 



