VOL. LXXXI.] PHILOSOPHICAL TEANSACTIONS. 97 



The manner in which air and fire act upon the antimonial calx and phospho- 

 rated lime, I shall venture to conjecture. It is probable, that the calx of anti- 

 mony and phosphorated lime combine with each other. 1. Because it requires 

 the application of heat and air for a shorter space of time to separate the sul- 

 phur from a given quantity of antimony mixed with bone-ashes, than to produce 

 this effect on antimony by itself: nor can the speedy calcination of antimony 

 with bone-ashes be explained by supposing that the antimony can then bear more 

 heat without melting; for the difference in the degree of heat applied in the 2 

 cases is not, apparently, sufficient to account for the difference of the times re- 

 quired for desulphurating the antimony. 2. Because it appears that heat, ap- 

 plied to antimony in a considerable variety of degrees, and air for various spaces 

 of time, formed a calx very different in colour, fusibility, and other chemical 

 qualities, from that produced by calcining this metallic substance with bone-ashes. 

 The strongest confirmation perhaps, of the opinion that the antimonial calx and 

 phosphorated lime are chemically united together is, that however long the cal- 

 cination of the antimony and bone-ashes is continued in the open vessel, it will 

 only produce precisely the same substance, with respect to chemical properties, 

 that is produced the moment the sulphureous fumes cease. 



But why is a snow-white powder produced by exposing a mixture of calcined 

 antimony and bone-ashes to air and fire for a due length of time, and then ap- 

 plying a greater degree of fire in close vessels, whereas no such white powder is 

 formed by a mixture of any calx of antimony and bone-ashes, exposed to any 

 degree of fire in close vessels, without previous exposure to fire and air ? The 

 reason may be, that in order that the calx should unite with the phosphorated 

 lime, it must be calcined to one certain degree ; which is effected by exposure to 

 air and fire with the bone-ashes when it can part or combine with air, so as to be 

 reduced to that state in which it will be duly calcined for union with that sub- 

 stance, which could not happen in close vessels. 



If it be objected, that this explanation does not account for the whiteness of 

 this preparation, which is only produced by a white heat, and to which air is not 

 necessary, the difficulty will be removed by considering that this whiteness may 

 be induced without any chemical alteration effected by the fire : for, after the 

 first calcination in the open vessel, it seems to act principally in the same way 

 that it does in making grey coloured bone-ashes, or imperfectly burnt bone, of 

 a snowy whiteness, namely, by totally destroying matter extraneous to the 

 phosphoric selenite. Fire also, in many instances, alters the colqur of bodies 

 without occasioning any change in their composition ; and perhaps the change 

 of the light clay or cineritious powder, -formed by the calcination of antimony 

 and bone-aslies in open vessels, to a snowy-white substance by further exposure 

 to fire, depends in part on its increase of specific gravity or other mechanical 



VOL. XVII. • O 



