COMPOSITION OF ORGANIC COMPOUNDS 45 



(2) In the case of a base : 



Organic bases form double salts with metallic salts, such as platinum 

 chloride, mercuric chloride. On heating the double salt in a crucible, 

 a residue of the metal is left. The estimation of the amount of metal 

 in a known weight of the compound gives the molecular weight. 



Ammonia and platinum chloride give the compound ammonio- 

 platinum chloride, 



(NH 3 . HC1) 2 . PtCl 4 . 



The organic bases form analogous compounds, the base replacing 

 the ammonia. Their general formula is therefore 

 (B . HC1) 2 . PtCl 4 or B 2 . H 2 PtCl 6 . 



The molecular weight of 2 molecules of base is thus 



B 2 . H 2 PtCl 6 - H 2 PtCl 6 . 

 e.g. x gm. of salt ga.vey gm. of platinum. 

 .'. 194-8 gm. platinum will be given by X -^ ^Uf gm. salt B 2 . 



Now 194-8 gm. platinum are contained in 409-8 gm. H 2 PtCl 6 . 

 ... ^g4 >8 xj* _ 40g .g i s t he molecular weight of B 2 . 



I94>8 X * - 409-8 



Hence molecular weight of i molecule of base is 



The gold salts have the general formula, 



B . HC1 . AuCl 3 or BHAuCl 4 , 

 from which the molecular weight of the base is calculated in a similar 



way. 



