860 Prof. J. Joly on the 



however, but little affected. This again illustrates how 

 independently the constituent molecules behave under the 

 influence of rising temperature. 



From these results we must conclude — contrary to what 

 I think would have been anticipated — that a compound of 

 antimony of the form n RS, m >Sb 2 S 3 becomes unstable in 

 presence of oxygen at a temperature which is unaffected by 

 the nature of R or the values of n or m. 



It would also appear from the results Nos. 21-25 that 

 other antimony molecules besides the sesquisulphide break 

 up at about this temperature, and that whether sulphur is 

 present or not. The observation of the temperature of sub- 

 limation of antimony from allemontite is rendered difficult 

 by the rapid evolution of arsenious oxide which precedes the 

 sublimation of the antimony. I found it, indeed, possible to 

 distill off: the whole of the arsenic leaving the antimony 

 almost in entirety on the hob, and in this manner to quanti- 

 tatively verify the constitution of the specimen. 



It is a rather remarkable feature of these observations that 

 the temperature of sublimation of the free element is higher, 

 sensibly, than that observed in the case of some of the com- 

 pounds examined. This seems to indicate that a certain 

 influence on the temperature of sublimation arises from the 

 presence of a more volatile atom. So far as the few obser- 

 vations go, the temperature of break-up is not appreciably 

 raised when the combined atom is more stable. Thus NiSb 

 breaks up at 500° and Ag 3 Sb at 520°. This observation 

 renders the high temperatures of sublimation of Nos. 18 

 and 19 the more remarkable. 



Arsenic. 

 The difference between the behaviour of arsenic and anti- 

 mony as volatile constituents of the molecule is interesting. 

 The break-up of the arsenic-bearing compounds appears to 

 be influenced by the molecular structure, so that these bodies 

 fall into groups defined by very different sublimation tem- 

 peratures. The number of experiments is small but they 

 stand, so far as my observations go, without exception to the 

 general principles which I have ventured to found upon 

 them. Such exceptions as at first seemed to exist were in 

 every case found explicable either on erroneous identifica- 

 tion or were removed by the adoption in one or two cases 

 of alternative and, I believe, more probable formulae. In 

 some respects the grouping must be regarded as provisional 

 only. 



