Thomson's System of Chemistry. 165 



His sections on the combination of gases (and indeed the 

 whole of this part of his work) are, with trivial alterations, 

 reprinted from the former edition, and are for the most part, a 

 repetition of what is given, with sufficient prolixity, in the first 

 volume. We should like to know the use of reprinting, at the 

 present day, Mr. Kirwan's table as one that " exhibits the 

 increase of density which takes place, when sulphuric acid of 

 the specific gravity 2.000 is mixed with various proportions 

 of water by weight?" He is well aware, that this ingenious, 

 but multifarious chemist, must have either operated on an 

 acid excessively contaminated with saline matter, or that his 

 numbers are hypothetical ; and his results are very inaccurate. 

 Dr. Thomson could have found, if he had chosen to look into 

 the pages of this Journal, modern tables, from which it appears, 

 that 50 of sulphuric acid + 50 of water give 0.107, for the 

 increase of density by combination, and not 0.1333, as he takes 

 it from Mr. Kirwan. 



In like manner, he occupies a great many pages with Has- 

 senfratz's tables of saline solutions, " which exhibit," he says, 

 " the specific gravity of saline solutions, differently impregnated, 

 at the temperature of 55° *." Here we find the specific gravity 

 of the saturated solution of sulphate of soda, the first in the 

 list, to be 1.060, a density which we know to be much too 

 small. The Doctor's fondness to involve questions of plain 

 arithmetic, in algebraic symbols and formate, appears in 

 the following passage : " Let D be the weight of a saturated 

 solution which we wish to dilute, S the quantity of salt which 

 it contains ; x, the quantity of water to be added ; S' the quan- 

 tity of salt contained in 100 parts of the new mixture; then we 

 have 



D + X D , SD-S'D 



hence x ■=. 



S S' S' 



Suppose the solution which we have, to be nitre, and 



D = 100. From the table we see that a saturated solution of 



nitre, contains 24.88 per cent of salt ; therefore S := 24,88. 



Let it be required to reduce it, so that it shall only contain 10 



per cent, of salt, here S' = 10. We have therefore, 



2488 - 1000 

 X = — ^^ = 148.8 



So that to 100 parts of the saturated solution, if we add, 

 148.8 parts of water by weight, we shall form a new solu- 

 tion, containing only 10 per cent of saltf." The formula is 

 taken from Hassenfratz, but the tautology is his own. The 

 Professor should observe the Horatian precept. Nee Deus 

 Intersil. A simple statement of proportion would place the 

 thing much more clearly before the :^tiidt'ut, and bring him, as 



• Si/stciii, III., 93. t Ibid., HI. 100. 



