200 



foot, at a speed of one mile per hour ; increasing, for greater velo- 

 cities, in a ratio considerably higher than the square of the velocity. 



The author concludes with some observations on the results lately 

 obtained in Scotland, where great velocities were given to boats 

 moving on canals, without a proportional increase of resistance. 



The reading of a paper, entitled, " Researches on the Arseniates, 

 Phosphates, and Modifications of Phosphoric Acid," by Thomas Gra- 

 ham, Esq., M.A., F.R.S.E., Lecturer on Chemistry in the Andersonian 

 Institution of Glasgow ; communicated by Edward Turner, M.D., 

 F.R.S. — was commenced. 



June 13, 1833. 



HIS ROYAL HIGHNESS THE DUKE OF SUSSEX, K.G., 

 President, in the Chair. 



Mr. Graham's paper was resumed and concluded. 



The tendency of the arsenic and phosphoric acids to form subses- 

 quisalts with the oxides of silver and lead is well known ; correspond- 

 ing salts with alkaline bases also exist. The author describes the me- 

 thod of forming the subarseniate and subphosphate of soda, and their 

 properties ; and shows that they are subsesquisalts, containing one 

 proportion and a half of base to one of acid. They are the only known 

 soluble salts of that constitution j and it is remarkable, that the acid 

 of the subphosphate of soda is not convertible into pyrophosphoric 

 acid by the action of heat, like the acid of the common phosphate of 

 soda. This may be explained on the hypothesis, that phosphoric acid, 

 in contradistinction to pyrophosphoric acid, contains an atom of water, 

 which stands in a basic relation to the acid, and which may be re- 

 placed by an atom of any of the usual bases. Hence also arises the 

 disposition of phosphoric acid to form subsesquisalts j for the common 

 phosphate, used as a precipitant, exchanges its basic water for a fixed 

 base ; and for this reason, likewise, phosphate of soda, or any neutral 

 phosphate, cannot be made anhydrous without becoming a pyro- 

 phosphate 5 but the subphosphates having an excess of base, may be 

 anhydrous, as Stromeyer observed ; and indeed they are not con- 

 vertible into pyrosalts. The acid formed by the combustion of phos- 

 phorus in air or oxygen, constitutes a third modification of phosphoric 

 acid, distinguished by peculiar properties, and which, from the differ- 

 ence of its saturating power, in relation to that of the phosphoric and 

 pyrophosphoric acid, the author considers as a polymeric phosphoric 

 acid ; — a term lately applied by Berzelius to bodies of the same rela- 

 tive composition, but differing in their combining proportions. 



The author devoted much time and attention to determine the quan- 

 tity of water of combination in the foregoing subsalts ; but the result 

 he obtained, namely 50 22 per cent., is not easily reconciled with our 

 best data for atomic weights. It is, however, pretty nearly compatible 

 with 23 or 24 atoms of water, according to Berzelius's weight ot the 

 atom of arsenic ; and if the latter estimate be correct, it is curious 



