508 POWDERS WITH A NITEATE BASE. 



4. On the contrary, the transformations yielding the maximum 

 of sulphate, that is to say, the following system : 



Eq. (1) X + eq. (2) x i 4- eq. (4) X J + eq. (5) X ^ 



should have produced, for 1238 grms. of matter, 853 Cal., and 

 321 litres of gas ; or, for 1 kgm., 689 Cal. and 259 litres. 



5. But the heat calculated as corresponding to the preceding 

 transformations is greatly too small. In short, we neglected in 

 the calculation 



1st. The change of the sulphide into trisulphide, which 

 liberates about -f 6 Cal. per equivalent. 



2nd. The change of an appreciable portion of carbonic acid 

 into bicarbonate, under the influence of a portion of the water 

 (1 per cent.), contained in powder a reaction unnoticed in theo- 

 retical equations neglecting the presence of water. 



This quantity, moreover, can hardly exceed 2 per cent. ; that 

 is to say, about an equivalent, being limited by the weight of 

 the water itself as well as by the quantity of the latter, which 

 produces sulphuretted hydrogen. Nevertheless this might add 

 further + 124 Cal. ' 



3rd. A portion of the sulphur, instead of producing potassium 

 trisulphide, was changed into iron sulphide, which liberates per 

 equivalent of sulphur 



F-f S = FeS,4-ll'9Cal. 



If the whole of the excess of sulphur assumed this form, we 

 might therefore have a thermal excess of + 47'6 Cal., and even 

 more, owing to the formation of a double iron and potassium 

 sulphide. The real figure is lower, the sulphur being by no 

 means all changed into iron sulphide, but it is impossible to 

 determine it for want of data. 



4th. The heat of combustion of carbon has here been calculated 

 supposing it pure, and even in the diamond state. In reality 

 the figure thus calculated is too low by an amount which may 

 be regarded as compromised between 1*5 Cal. . (pure carbon 

 derived from charcoal) and 5 '2 (bakers' embers), for 1 eq. 

 (6 grms.) of carbon. This makes for 964 grms. of powder a 

 thermal excess comprised between 31 '5 Cal. and 109'2 Cal. It 

 is true that this error is partly compensated, because we have 

 taken the weight of real carbon as equal to the weight of 

 charcoal, while it is less by about a fourth (see p. 488). 



However this may be, we see from this that the error in the 

 number above calculated (674*5 Cal.) might amount in an 

 extreme case to 



109-2 + 47-6 + 12-4 = 169-2, 



which would make in all 8437 Cal., or an excess of a fourth in 

 the number calculated. 



The real excess, under the conditions of the experiment of 



