254 INORGANIC CHEMISTRY 



500 amperes and 70 volts, a fused mass of yellow nitride is obtained; 

 while the high temperature of an arc of 1200 amperes and 70 volts 

 gives a carbide of titanium free from nitrogen. With so intense a 

 current as this last the nitride of titanium can no longer be formed; 

 its dissociation by heat is complete and only the carbide can remain. 



In pursuing this study, we have found still other examples of 

 combination and then decomposition under the action of an electric 

 arc of greater and greater intensity. 



Organic chemistry comes into contact with biology; whence its 

 greatness and also its difficulties. 



Biological chemistry could not be developed till after a systematic 

 study of the chemistry of carbon had been made. For a century it 

 was thought that physiological chemistry needed in its manifold 

 transformations only the four elements, carbon, hydrogen, nitrogen, 

 and oxygen. But in recent years our ideas on this point have changed 

 considerably. It has long been known that iron was indispensable in 

 both the animal and vegetable kingdoms. Further, Raulin had proved 

 by some curious experiments the important influence of traces of 

 foreign metals on the culture of aspergillus niger. These experiments 

 had been forgotten; they came too early. 



But to-day discoveries relating to this point appear in constantly 

 greater numbers. For example, the fine work of Frederick and of 

 Henze has shown that copper is a constituent of hemocyanin in the 

 blood of cuttlefishes and Crustacea. We know now that iodin and 

 bromin should be found in the thyroid gland; these elements are 

 seen to be indispensable to the regular course of normal life. The 

 existence of arsenic in animal tissues was a thing unheard of a few 

 years ago. Professor Armand Gautier has now established by very 

 delicate experiments that arsenic is always present in the horny 

 tissues and in the thyroid gland; and M. Gabriel Bertrand has 

 demonstrated the normal existence of arsenic in the living cells of 

 fishes taken from the sea-bottom at a depth of 3000 meters. 



In the same way, a trace of another element, such as manganese, 

 may intervene in the form of a soluble ferment, in the oxydases. One 

 understands then the importance of the different elements and sees 

 that sometimes, in traces, they may play a physiological role of 

 capital importance. We have long known that sulphur forms part 

 of the proteid molecule, although we are still quite ignorant of the 

 transformations which bring this element into complex compounds. 

 It is quite evident that on this point great discoveries still await 

 their realization. We are only beginning to-day the study of the dif- 

 ferent elements in their combinations with carbon, from the physio- 

 logical point of view; it may be said that the physiology of the cell 

 remains wholly to be made. We are happy to know that a start in 

 this direction is being made by means of microchemical reactions. 



