62 Scientific Intelligence. 



The analogy of the tribasic and bibasic acids leads for citric 

 acid to the formula, tJgH^e^ . 3011, while the 'formulas for the 

 three modifications of phosphoric acid would be the following : 



HPOg.^^, 2HPe3.jJ^, lire,, 



by which the thermic difference between citric acid and the acids 

 of phosphorus and arsenic may be explained in harmony with the 

 prevalent chemical theories. 



(9.) Silicic acid is given in the tables (accompanying this paper) 

 as a bibasic acid, but differs materially from the other acids of this 

 group, by being absolutely without any definite point of neutrali- 

 zation. The numbers of table II show, it is true, that the beat 

 which a molecule of the acid evolves with an increasing quantity 

 of soda, increases only very slightly when this exceeds two mole- 

 cules of sodic hydrate, and table I shows that the evolution of heat 

 increases approximately in proportion to the quantity of acid, 

 until this amounts to | molecule of silicic acid for one molecule of 

 sodic hydrate. But table II shows at the same time that the num- 

 bers by no means increase in proportion to the quantity of soda, 

 and table I also shows that the evolution of heat increases very ma- 

 terially for further additions of silicic acid. From what was shown 

 in Section IV (Pogg. Ann., Bd. 137, p. 203), it appears that the 

 maximum of heat which a molecule of sodic hydrate can evolve 

 with silicic acid, and which occurs only when the quantity of acid 

 is infinitely great, amounts to 134 . . while for ^ molecule of silica 

 it is only 26 . . ; fiirther, that the maximum of heat which is 

 evolved by the action of a molecule of silica upon sodic hydrate, 

 and which also occurs when the quantity of sodic hydrate becomes 

 infinitely great, amounts to only 63 . . while two molecules of sodic 

 hydrate already evolve 52 . . . 



(10.) The anomaly in the neutralization of silica has very prob- 

 ably its cause in the simultaneons action of water and silica upon 

 sodic hydrate, xiccording to what has been sai.l under 4, water is 



dium saft. If now the sodium salt' is attac-kcd simultaneously by 

 the two acids (water and silica), the base divides itself between 

 the two acids in a ratio which depends upon the avidity of the 

 acids and their quantity, (see Sect. 1, Pogg. Ann., Bd. 138, p. 94)- 

 If now the avidity of the water for the base is very small in com- 

 parison with that of the acid, this decomposes an approximately 

 equivalent quantity of sodic hydrate, and the evolution of heat 

 becomes therefore approximately proportional to the quantity oi 

 acid, as is also approximately the case with all other acids. W? ,*^° 

 the contrary, the avidity of the water for the base is a quantity 

 which cannot be neglected in comparison with that of the acid, 

 the proportionality in the evolution of heat ceases, and then wl- 



ty in 

 1 holds 



ited). The 



good for partial decomposititfn, (see reier- 

 ■ '• of heat which takes place when a 



of sodic silicate (and also various other saline solutions) is 

 vith water, ' - - - - - - --' ^ 



composition of the s 



uted with water, has probably its cause partly in a partial <i 

 ■ ■ " ' i salt by the wat 



