Church — On Native Phosphates of Aluminium. 551 



LXXYI. — On" the Constitittion op the ITatite Phosphates op 

 Alumbstitim. By A. H. Chuech, M.A., Oxon., Professor of 

 Chemistry in the Eoyal Academy of Arts. 



[Eead, February 27, 1882.] 



§1. The mineral phosphates and arseniates constitnte a very interest- 

 ing group. The number of species is increased year by year through 

 new discoveries ; but the older members of the group are rarely made 

 the subjects of fresh investigation by modern methods. In many 

 instances the constitution of even the more abundant species remains 

 obscure. The frequent presence of an excess of base over that 

 required for an orthophosphate is a common characteristic of the 

 group. Another prominent feature consists in the peculiar and 

 diverse modes in which the water present in the hydrated species 

 is held. Por several reasons the moderate-sized group of the hy- 

 drated aluminium phosphates has been selected for renewed investiga- 

 tion. Light has been thrown upon the relations of these compounds 

 by accurate analyses, in which a special and uniform method of 

 desiccation has been adopted ; in which silver vessels have been sub- 

 stituted, where deemed preferable, for those of glass and porcelain; 

 and in which sodium hydrate, from metallic sodium, has been used, 

 instead of alcoholic potash, for retaining alumina in solution. The 

 present communication contains an account of a considerable number 

 of analyses conducted with the precautions named above; but it 

 does not pretend to offer an exhaustive treatment of the subject, 

 nor a decisive opinion upon all the questions of chemical constitu- 

 tion involved in the inquiry. 



§ II. As a preliminary step towards the discovery of the constitu- 

 tion of the hydrated aluminium phosphates, it was deemed expedient 

 to ascertain with what tenacity the normal native aluminium hydrate 

 and the normal native aluminium phosphate respectively retained their 

 water. This mode of experimenting was expected to disclose how far 

 that common assumption could be correct which attributed to the native 

 basic aluminium phosphates such a formula as — 



xAlgPaOg, yAlgHsOe, z aq. 



Fortunately a suitable native hydrate and native phosphate are 

 known ; the former being the gibbsite of Dana, now often called 

 hydrargillite ; the latter being the variscite of Breithaupt. 



§111. Gihhsite. — On submitting gibbsite to the process of desic- 

 cation, the mineral retained the whole of its moisture, not only in 

 dry air and in vacuo, but also at 100° C. in the air-oven. The analyti- 

 cal details are here given : — 



R. I. A. PROC, SEE. II. VOL, III. — 6CIENCE. 2 Z 



