PKOFESSOE THOMAS GRAHAm's SCIENTIFIC WORK. 183 



accompanied correlatively by the forination of a strongly acid liquid 

 According- to Berzelins, the ratio of the oxygen of the base to that of 

 the acid, in this yellow ])recii)itate, was as 3 to 5. 



In ISlil Mitscherlich, then working in Berzelius's laboratory, obtained, 

 by treating ordinar^^ phosphate of soda with aqueous phosphoric acid, 

 a new crystallizable phosphate of soda, in which the ratio of acid to 

 base was twice as great as that in the ordinary phosphate. This new 

 salt, which had a strongly acid reaction to test paper, he called the bi- 

 phos[)hate of soda. He observed that it was a hydrated salt, and that 

 while the ratio in it of the oxygen of the base to the oxygen of the acid, 

 was as 1 to 5, the ratio of the oxygen of the base to the oxygen of the 

 water was 1 to 2. 



In ]827 Mr. Graham's fellow-townsman, and predecessor at the Me-, 

 chanics' Institute, Dr. Clark, discovered another new phosphate of soda, 

 in which the ratio of the oxygen of the base to the oxygen of the acid 

 was identical with that in the ordinary phosphate, namely, as 2 to 5. 

 But whereas the or<linary phosphate crystallized with 25 proportions of 

 water, the new phosphate crystallized with only 10; and whereas the 

 ordinary phosphate gave a yellow precipitate with nitrate of silver and 

 a strongly acid supernatant liquid, the new i)hosphate gave a chalk- 

 white precipitate with nitrate of silver and a perfectly neutral superna- 

 tant liquid. This new phosphate, being formed by heatnig the common 

 phosphate to redness, was accordingly designated the pyroi)hos})hate. 

 By dissolution in water and evaporation of the liquid, it could be ob- 

 tained in the lOhydrated crystalline state; and by desiccation at a 

 sand-bath heat, the crystalline salt could be again rendered anhydrous. 

 With regard to the 25 proportions of water belonging to the ordinary 

 salt, Dr. Clark noti(5ed that 24 proportions could be driven oft" by a sand- 

 bath heat, and that this moderate heat did not alter the nature of the 

 salt. He found that the 25th proportion of water, however, could only 

 be driven oft by a full red heat ; and that, simultaneously with its ex- 

 pulsion, the change in the nature of the salt was effected. But he care- 

 fully guarded himself against being supposed to think that the change 

 in properties of the salt was consequent upon an elimination of its 

 water. The driving off of water from salts being, as he justly remarked, 

 a common effect of heat, he regarded this effect as a concomitant only 

 of the peculiar effect of heat in altering the nature of the phosphate. 



Other anomalies with regard to phosphoric acid and the phosphates 

 were also known to chemists; and, on referring now to standard chem- 

 ical works written before the year 1S33, the whole subject of the phos- 

 phates will be seen to be in the greatest confusion. It was in this year 

 that Mr. Graham communicated his paper, entitled " Researches on the 

 arseniates, phosphates, and modifications of phosphoric acid," to the 

 Royal Society.* 



In the course of these researches he established the existence of a 



* Philosophical Transactions, 1833, p. Ji53. 



