ON CHEMICAL NOMENCLATURE. 73 



The employment of such terms as ' Phosphorsuperchloriir,' ' iuter- 

 mcdiarer Cblorphosphor ' for the trichloride, and the corresponding 

 ' Phosphorsuperchlorid,' ' Chlorphosphorsepim maximum ' for the penta- 

 chloride, is explained by the fact that a solution of phosphorus in the 

 trichloride was formerly supposed to be a lower chloride of phosphorus, 

 ' Phosphorcbloriir,' ' Chlorphosphor iin minimum.' 



The following observations relate to the prevalence of certain names at 

 different periods : — 



1. Anhydrous Phosphorous Acid was formerly called phosphorous acid ; it 

 is now usually called phosphorous anhydride, and to a le c s extent phos- 

 phorus trioxide. 



2. Hydric Phosphite was called (when obtained from trichloride of 

 phosphorus and water) a compound of phosphorous acid and water. 

 From 1840 till 1800 it was called hydrate of phosphorous acid or hydrated 

 phosphorous acid. It is now called phosphorous acid. The term hydric 

 phosphite has been very seldom used. 



3. Anhydrous Phosphoric Acid was originally called phosphoric acid ; it 

 is now usually called phosphoric anhydride, and to a less extent phos- 

 phorus pentoxide. The term anhydrous phosphoric acid has been fre- 

 quent^' employed. 



4. Hydric Phosphate was called hydrate of phosphoric acid or hydrated 

 phosphoric acid till 1800 ; it is now called phosphoric acid. The term 

 hydric phosphate has been seldom used. 



5. Trichloride of Phosphorus. — The terms protochloride of phosphorus 

 and phosphorous chloride (or Phosphorcloriir) were of equal prevalence 

 till 1868, when the former expired. Trichloride of phosphorus is the 

 name now chiefly used. 



6. Similar remarks apply to peniachlorule of phosphorus, except that the 

 term perchloride of phosphorus has been more largely used than phos- 

 phoric chloride, although it expired in 1808. 



TABLE XI. 



In this table we find that the names 'chloride of copper,' ' dichloride 

 of copper,' and ' protochloride of copper,' have all been applied to the 

 lower chloride, and the names 'chloride of copper,' ' deutochloride,' 

 'bichloride,' and 'protochloride of copper,' have all been applied to the 

 higher chloride. Th. Thomson introduced the names proto- and deuto- 

 chloride for the 1st and 2nd chloride respectively, but later on he adopted 

 the names subchloride and chloride. Brande, in the first edition of his 

 ' Chemistry,' calls the two bodies chloride and bichloride of copper, but 

 in his 6th edition we find the names dichloride and protochloride, signify- 

 ing that the first has two atoms of copper and the second one. Some 

 chemists have followed this rule, others the system of Thomson, so that 

 while Brande, Watts, Regnault, and Bernays apply the name protochloride 

 to the higher body, Thomson, Thenard, Gay-Lussac, Naquet, and Har- 

 court apply the same name to the lower body. 



General Remarks on the Preliminary Report. 



The usefulness of any system of nomenclature rests mainly on its 

 permanence. 



The tables in this Report, summarising the history of the nomen- 

 clature of certain typical chemical compounds, clearly indicate the 

 conditions most essential for permanence. Names have been given to 

 bodies expressing particular opinions on their ultimate constitution, whilst 

 other names have been given expressing no theoretical views, but simply 



