wi^^r-y 



m 



iiEroRT — J8S4. 



I 



TABLES VIII.-X. 



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

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

 acid, and hypophosphorous acid were formerly exclusively employed to 

 denote the oxides, but are now chiefly nsed 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 done by ascribinpf them to differences 

 in the arrangement of atoms in tno group PjO;,. When, therefore, the 

 older cliemists speak of the different varieties of phosphoi-ic acid, it is the 

 anhydrous acid that they mean. For instance, Berzelius's a, (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, P4O. (Gmelin, edited by Watts, 184'J). 



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

 phosphate and hydrodisodic phosphate. Diphosphate of soda has been 

 applied to trisjdic and hydrodisodic phosphates, and biphosphate to 

 dihydrosodic phosphate, so that the thi'ee phosphates have had almost 

 identical names. 



Tiio term ' acid phosphate ot soda ' has been applied to both hydro- 

 disodic and dihydrosodic phosphates. 



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

 phosphorus. (Cf. Liebig and Poggendorff'.) 



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 :aid 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 : 



■ J 



Thus : 



bi- to multiply the acid, 

 di- to multiply the base. 



Na20.2Si02, bisilicato of soda. 

 2Na20.Si0.2, disilicate of soda. 



might have been 



The prefixes * tor-' and'ti'i-,' ' quater-' and ' tetra- 

 employed in the same way, e.g. : — 



NajO.SSiO.j, tersilicate of soda. 

 oNajO.SiO.j, trisilicato of soda. 

 Ca4H(P04)3, totracalcic terphosphate. 

 Ca3(PO|)2, calcic triphosphate. 



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



(Continued on p. 73.) 



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