32 PROCEEDINGS OF THE AMERICAN ACADEMY 



temperatures into dimethylamine and the following compound, — a 

 decomposition which is hastened by heat. 



Tridimethylamine Disilicotetrafluoride, ((CH 3 ) 2 NH),(SiF 4 ) 2 . — This 

 substance was made by subliming the compound just described, when 

 dimethylamine was given off as a secondary product. It was purified 

 by a second sublimation, and its composition determined by the fol- 

 lowing analyses. 



I. 0.1871 grm. of the substance gave 0.0660 grm. of silicic dioxide. 

 II. 0.2800 grm. of the substance gave 0.0960 grm. of silicic dioxide 

 and 0.2694 grm. of sodic fluoride. 



Properties. — It is a white powder resembling the corresponding 

 aniline compound in appearance and behavior when heated, although 

 it sublimes at a higher temperature. It also differs from the aniline 

 compound in being deliquescent. 



Finally, we may add the following experiments, which gave pro- 

 ducts of so little promise that we did not attempt to analyze them, 

 but which show that fluoride of silicon acts also on alkaloids, and on 

 amides which can form salts. 



Fur/urine, when treated in benzol solution with fluoride of silicon, 

 gave a gummy mass similar to that obtained from dimethylaniline, 

 which however did not crystallize on standing. 



Dry powdered urea was converted by fluoride of silicon into a pasty 

 mass, which was decomposed with evolution of ammonia, when the 

 attempt was made to sublime it. The sublimate contained fluorine 

 and silicon, but we did not continue the study of it, as we had no 

 guaranty that it was a homogeneous substance. 



Constitution op the Silicotetrafltjorides. 



Although we have not succeeded in obtaining an absolute direct 

 proof of the constitution of the substances described in this paper, 

 we have been able to reduce the possible formulas that can be as- 

 signed to them to a very small number by the following course of 

 reasoning. In the first place, we assume that all the substances 

 described in this paper, which contain three molecules of the base 

 combined with two of fluoride of silicon, have the same constitution, 

 an assumption which is justified by the fact that they are all made 



