xx DISSOCIATION 519 



gas required to convert the same weight of potassium into 

 chloride were 



2 volumes of chlorine gas, 

 4 volumes of hydrogen chloride gas, 

 and 8 volumes of sal-ammoniac. 



The first three observations can be explained by 

 Avogadro's hypothesis as expressed by the equations : 

 4K + O, (i vol.) =2K 2 O 



4K + 2C1, (2 vols.) =4KC1 

 4 K + 4HC1 (4 vols.) = 4 KC1 + 2H 2 . 



But the case of sal-ammoniac is quite anomalous, since 

 Avogadro's hypothesis would indicate that only four volumes 

 of the gas were required, as shown by the equation : 

 4 K + 4 NH 4 C1 (4 vols.) - 4KC1 + 4NH 3 + 2H 2 . 

 A similar anomaly was observed in the vapour-densities of 

 the ammonium and phosphonium salts examined by Bineau 

 in 1838 (Ann. Chim. P/iys., 1838, 68, 416-441). 

 The following compounds were studied : 



PH 3 + HI = PH 4 I (phosphonium iodide) 

 PH 3 + HBr = PH 4 Br (phosphonium bromide) 

 2NH 3 + CO.j =(NH 3 ) 2 CO 2 (ammonium carbamate) 1 

 NH 3 + SH 2 = NH 4 HS (ammonium hydrosulphide) 

 NH 3 + HCN =NH 4 CN (ammonium cyanide) 

 NH 8 + HC1 - NH 4 C1 (ammonium chloride) 



In each case an easily crystallised compound was formed, 

 but a study of the vapour showed that no contraction in 

 volume had taken place. Thus Bineau found that 

 phosphonium iodide "is formed from equal volumes of 

 phosphoretted hydrogen and hydriodic acid united without 

 condensation, and that its density, in the state of vapour, is 

 the mean of the densities of its components " (foe. cit. 

 p. 430.) 



1 The product "sal-volatile" is not a true carbonate, but the 

 ammonium salt of carbamic acid, NH 2 *CO*OH ; compare p. 430. 



