712 REPOET— 1893. 



in tlie way have not obtained results of a very conclusive kind. It is known that 

 the product when strongly heated in a current of ammonia gas affords ammonium 

 chloride, which volatilises, and a residue, to which Schutzenherger and Colsonhave 

 assigned the formula SioN^H. This body they regard as a definite hydride of 

 SioNj, which latter they produced by acting on silicon at a white heat with pure 

 nitrogen. Gattermann suggests that a nearer approach to the silicon analogue of 

 cyanogen, Si.,N,,, should be obtained from the product of the action of ammonia on 

 silicon-chloroform ; but it does not appear that this suggestion has yet borne fruit. 

 It was scarcely probable that the above-mentioned rather indefinite compounds of 

 silicon with nitrogen were the only ones of the class obtainable, since bodies includ- 

 ing carbon combined with nitrogen are not only numerous but are among the most 

 important carbon compounds known. Further investigation was therefore neces- 

 sary in the interests of comparative chemistry, and for special reasons which will 

 appear later on ; but it was evident that a new point of attack must be found. 



A preliminary experimental survey proved the possibility of forming numerous 

 compounds of silicon containing nitrogen, and enabled me to select those which 

 seemed most likely to afford definite information. For much of this kind of work 

 silicon chloride was rather too energetic, hence I had a considerable quantity of 

 the more manageable silicon tetrabromide prepared by Serullas' method, viz., by 

 passing the vapour of crude bromine (containing a little chlorine) over a strongly 

 heated mixture of silica and charcoal. In purifying this product I obtained inci- 

 dentally the chloro-bromide of silicon, SiClBrg, which was required in order to 

 complete the series of possible chlorobromides of silicon.^ 



Silicon bromide was found to produce addition compounds very readily with 

 many feebly basic substances containing nitrogen. But one group of bromides 

 of this class has yet been investigated in detail, namely, the products aflforded by 

 thioureas. The typical member of this group is the perfectly definite but uncrys- 

 talline substance 



SiBr /(CSN,,H,),Br 



Substituted thioureas afford similar bodies, the most interesting of which is the 

 allyl compound. This is a singularly viscid liquid, which requires several days at 

 ordinary temperatures to regain its level, when a tube containing it is inverted. 

 But these are essentially addition compounds, and are therefore comparatively un- 

 important. 



In most cases, however, the silicon haloids enter into very definite reaction with 

 nitrogen compounds, especially when the latter are distinctly basic, such as aniline 

 cr any of its homologues. One of the principal products of this class of change is 

 the beautiful typical substance on the table, which is the first well-defined crystal- 

 line compound obtained in which silicon is exclusively combined with nitrogen. 

 Its composition is Si(NHC^Il5)4.'" Analogous compounds have been formed with the 

 toluidines, naphthylaminea, &c., and have been examined in considerable detail, 

 but it suffices to mention them and proceed to point out the nature of the changes 

 we can effect by the action of heat on the comparatively simple anilide. 



When silicon anilide is heated carefully in vacuo it loses one molecule of aniline 

 very easily and leaves triphenyl-guanidine, probably the a modification; if the 

 action of heat be continued, but at ordinary pressure and in a current of dry 

 hydrogen, another molecule of aniline can be expelled, and, just before the last 

 trace of the latter is removed, the previously liquid substance solidifies and affords 

 a silicon analogue of the insoluble modification of carbodiphenyldiimide, which 

 may then be heated moderately without undergoing further material change. A 

 comparison of the formulse will make the relations of the products clear : — 



Silicotetraphenylamide — Si(NHPh)4 

 Silicotriphenylguanidine— Si : NPh. (NHPh)., 

 SiUcodiphenyldiimide — Si : (NPh)^. 



' Three years later Besson formed the same compound and described it as new. 

 ^ Harden has obtained an uncrystalline intermediate compound, SiCl2(NHCsH5)2' 



