46 REroRT — 18S4. 



TABLES VIII.-X. 



From the above tables it -will be seen that many names have been used 

 in more than one sense. Thus the terms phosphoric acid, phosphorous 

 acid, and hypophosphorous acid were formerly exclusively employed to 

 denote the oxides, bat are now chiefly used to denote the hydrogen salts. 

 Graham's researches were published in 1833, and previous to this date 

 chemists made no distinction between anhydrous and hydrated phosphoric 

 acid, but called one phosphoric acid, the other a solution of phosphoric 

 acid ; hence, when it was necessary to explain the differences between 

 ortho- and pyro-phosphates, this was clone by ascribing them to differences 

 in the arrangement of atoms in the group P 2 5 . When, therefore, the 

 older chemists speak of the different varieties of phosphoric acid, it is the 

 anhydrous acid that they mean. For instance, Berzelius's u, (3, and y 

 phosphoric acids are all three regarded by him as anhydrous. The term 

 phosphoric oxide is applied to anhydrous phosphoric acid in the editions 

 of Fownes edited by Watts ; this term was formerly used to denote a sup- 

 posed lower oxide of phosphorus, P 4 0. (Gmelin, edited by Watts, 1849). 



The term 'neutral phosphate of soda' has been applied both to trisodic 

 phosphate and Lydrodisodic phosphate. Diphosphate of soda has been 

 applied to trisodic and hydrodisodic phosphates, and biphosphate to 

 dihydrosodic phosphate, so that the three phosphates have had almost 

 identical names. 



The term ' acid phosphate of soda' has been applied to both hydro- 

 disodic and dihydrosodic phosphates. 



The term ' phosphorchlorid ' has been applied to both chlorides of 

 phosphorus. (Cf. Liebig and PoggendorfT.) 



It appears that when a numerical prefix is employed, the number ought 

 to be understood as multiplying the word to which it is prefixed and not 

 some other word. This rule has often been violated : thus trisodic phos- 

 phate has been called ' triphosphate of soda,' also ' diphosphate of soda ' 

 and ' sesquiphosphate of soda ; ' in all these cases the prefix is intended 

 to indicate the number of molecules of soda to one molecule of phosphoric 

 acid. So Turner calls hydrodisodic phosphate and dihydrosodic phos- 

 phate, 'triphosphate of soda and basic water' and 'acid triphosphate of 

 soda and basic water ' respectively. 



It is to be observed, however, that in the older form of nomenclature 

 ambiguity was avoided in the case of compounds containing double the 

 usual amount of acid or of base by using the prefix : 



bi- to multiply the acid. 



di- to multiply the base. 

 Thus : 



!Na,0.2Si0 2 , bisilicate of soda. 

 2]SFa 2 O.Si0 2 , disilicate of soda. 



The prefixes ' ter-' and 'tri-,' ' quater-' and ' tetra-' might have been 

 employed in the same way, e.rj. : — 



Na 2 0.8Si0 2 , tersilicate of soda. 

 3Na 2 O.Si0 2 , trisilicate of soda. 

 Ca 4 H(P0 4 ) 3 , tetracalcic terphosphate. 

 Ca 3 (P0 4 ) 2 , calcic triphosphate. 



But satisfactory evidence that they were so used has not been found. 



(Continued on p. 73.) 



