632 PROF. F. GUTHRIE ON SOME DERIVATIVES FROM THE OLEFINES. 
Consequently, the isotypes and idiotypes of one and the same body are related to 
one another as an atom complex is to an atom simple. 
Certain of the bodies were procured in too small a quantity for their specific 
gravities to be taken in the ordinary method. When this was the case, and the 
substances were insoluble in water, a solution of nitrate of ammonia, or of chloride 
of calcium was so graduated by water, that a drop of the liquid under examina- 
tion remained in indifferent equilibrium in the saline solution. The specific 
gravity of the saline solution is then taken in the ordinary manner, and is of 
course identical with that of the liquid examined. 
I allow myself, in conclusion, to express a regret, that circumstances have 
prevented me from offering my results to the Society in a more elaborated form. 
I shall take the earliest opportunity of prosecuting this direction of research. 
Meanwhile, let me offer my thanks to Professor Roscor of Manchester, and Dr 
Prayrair of Edinburgh, for having allowed me to carry on my experiments in 
their laboratories. To Professor KoLBe in Marburg I am also indebted, for having 
on all occasions, placed the resources of his laboratory at my disposal. 
Eprinsuren University Laporarory, 
March 1861. 

