PROFESSOR THOMAS GRAHAm'S SCIENTIFIC WORK. 185 



base, will possess and retain for sometime the cliaracters of its peculiar 

 moditication. * * * But I suspecttliat the modifications of phosphoric 

 acid, when in what we would call a free state, are still in combination with 

 their usual proportion of base, and that that base is water. Thus the 

 three modifications of phosphoric evidence may be composed as follows : 



Phosphoric acid iH H O . P O 5. 



Pyrophos]ihoi'ic acid ., 2 H O . P 5- 



Metaphosphoiic acid- H O . P O 5.; 



or they are respectively a tri-phosphate, abi-phosphate, and jdiosphate 

 of water." These remarks he followed up by analytical evidence, show- 

 ing the existence of the three hydrates, each in its isolated state. 



Just as in his demonstration of the relationship to one another of 

 sub-phosphate of soda, phosphate of soda, bi-phosphate of soda, and 

 common i)hosphoric acid, Mr. Graham originated the notion of polybasic 

 compounds, so, in his demonstration of the nature of the pyrophosphates 

 and metaphosphates, as bodies difteiing from the normal compounds 

 by an abstraction of water or metallic base, did he originate the notion 

 of anhydro-compounds — so did he discover, for the first time, an in- 

 stance of that relationship between bodies which is now known to pre- 

 vail most extensively among products of organic as well as of mineral 

 origin. 



The different proi>erties manifested by phosphoric acid, in its differ- 

 ent reputedly isomeric states, having been shown by Mr. Graham to be 

 dependent on a difference of hydration; that is to say, on a difference 

 of chemical composition, he was inclined to view the difference of prop- 

 erties observed in the case of other reputedly isomeric bodies as being 

 also dependent on a difference of composition, the difference occasionally 

 consisting in the presence of some minute disregarded impurity. Accord- 

 ingly he communicated to the Eoyal Society of Edinburgh in 1834* a 

 paper " On phosphureted hydrogen," in which he showed that the spon- 

 taneously inflammable and non-spontaneously inflammable varieties of 

 the gas " are not isomeric bodies, but that the peculiarities of the spon- 

 taneously inflammable species depend upon the presence of adventitious 

 matter," removable in various ways, and existing but in very minute 

 l^roportion.t He further showed that the vapor of some acid of nitro- 

 gen, apparently " nitrons acid, is capable of rendering phosphureted 

 hydrogen spontaneously inflannnable when present to the extent of one 

 ten-thousandth part of the volume of the gas." In connection with this 

 research may be mentioned Mr. Graham's earlier experiments on the 

 influence of minute impurities in modifying the chemical behavior of 

 different substances. In some " Observations on the oxidation of phos- 

 phorus," published in the Quarterly Journal of fScience,| for 1829, he 

 showed that the presence of ^i^ of olefiant gas, and even j^^, by vol- 



* Edinbnr<>h Royal Society Transactions, xiii, 183G, \). 88. 

 t It was afterward isolated by P. Tlienard. 

 i Quarterly Journal Science, ii, 1829, p. 83. 



