152 Scientific Intelligence. [Frx, 
as occasioned by the mutual decomposition of the two salts by 
each other.—(Ann. de Chim. et Phys. ix. 10.) 
XIV. Constituents of Saltpetre. 
{a late number of the Annals of Philosophy, Linserted a set 
of experiments on the analysis of this salt by Berthollet; and 
contrasted his results with those of Dr. Wollaston, and my own. 
These three sets of experiments were made in a different way. 
Dr. Wollaston saturated a given weight of bicarbonate of potash 
with nitric acid, and determined the weight of the nitre formed. 
Berthollet decomposed a given weight of saltpetre by heat, and 
measured the volume of oxygen and azotic gases evolved. I 
decomposed a given weight of nitre by sulphuric acid, and deter- 
mined the weight of the sulphate of potash formed. It is 
probable that none of these methods is susceptible of absolute 
precision. But if each of them were performed with as much 
accuracy as the experiment would admit, the mean of the results 
obtained by the three methods would, in all likelihood, give us 
the true: result. Dr. Wollaston’s method has been recently 
repeated by M. Longchamp. He found nitre composed of 
SYANIC) BOK oes Use bse aces Cas 53°297 
0) 3) a Se eae 46°703 
100:000 
(Ann, de Chim. et Phys. ix. 27.) 
This result does not differ much from that obtained by Dr. 
Wollaston ; namely, 
Te wis ee ere atest tbe aes 
Pistasite’s, eset, dagdin cde was 46-457 
100-000 
If an atom of nitric acid weigh 6:75, and an atom of potash 
6, as I conceive them to do, then the true composition of nitre 
must be, 
Aid RIGA PHA. PGES 583°726 
Potash eRe — . 46:274 
100-000 
Dr. Wollaston’s numbers approaching more nearly to these 
than the numbers given by Longchamp, I consider them as 
nearer the truth. Indeed Dr. Wollaston’s results do not differ 
stoth part from the theoretical composition of nitre. Now Iam 
afraid that it is scarcely possible to come nearer the truth than 
this by a single direct experiment. Chemical precision, like 
astronomical, can be looked for only from the mean of a great 
number of experiments so contrived that the errors must of 
necessity fall on different sides, 
