452 Notices respecting New Books. 



measure) of sulphuric acid to eight ounces by weight of nitre will 

 be found convenient proportions." In this short quotation there is 

 much to perplex a student; but "precise and minute directions" 

 for enabling him to perform the experiment are lamentably defi- 

 cient. The quantities which had been previously mentioned, we sup- 

 posed were intended for operations on the small scale, since flasks 

 are the vessels in which they are directed to be conducted ; and we 

 have heard of wine measure, beer measure, and imperial measure, 

 but we have yet to learn what water measure is. An ounce water 

 measure may, we conceive, have several meanings ; first, the measure 

 of an avoirdupois ounce of water j secondly, the fluid ounce used in 

 the London Pharmacopoeia ; and, thirdly, the measure of a troy 

 ounce of water : so that the student has the chance of using a 

 measure equal to 480, ^5^5, or 437'5 grains of water. Nor is this 

 all ; he is directed to take eight ounces of nitre, and " by weight," 

 for fear he should measure them ; but as to whether the ounces are 

 to be avoirdupois or troy weight, he is totally without a guide. As 

 however the quantities, whatever they may be, are specially di- 

 rected for the " small scale," the student may suppose that they 

 are to be as different as he can make them by the laxity of the rule, 

 from the proportions previously assigned : in this case he may 

 take the avoirdupois ounce of water for the measure of the acid, 

 and the troy ounce in weighing the nitre ; and then the weight of 

 the acid will be to that of the nitre about as 2 to 3*16, which are 

 indeed very nearly the quantities given in the Edinburgh Phar- 

 macopoeia, and proportions less in unison with the doctrine of equi- 

 valents could hardly be adopted : on one plan of operation the 

 quantity of sulphuric acid is too great, and that of the water which 

 it contains is too small on the other. 



Referring to the red acid, which is a mixture of nitric and ni- 

 trous acids, Mr. Reid says : " It is seldom necessary to expose the 

 mixed acid to heat so as to obtain pure and colourless nitric acid, as it 

 may be used for almost all the purposes to which the latter is applied. 

 It is even preferred in many processes from its great strength, being 

 always stronger and more active than the pale acid. Dr.Hope has 

 prepared it with so high a specific gravity as P54, though the spe- 

 cific gravity of the colourless acid does not exceed 1*500." Others 

 have obtained the red acid of a still higher specific gravity than 

 Dr. Hope ; but whatever may be its density, we deny that it is on 

 that account stronger than pale acid, nor are we aware that it is 

 more active ; and if it Were so, the proof would be difficult, for it is 

 never used as a solvent without previous dilution. 



When nitric oxide gas is passed into colourless nitric acid it be- 

 comes red, and its density is considerably increased : when, how- 

 ever, water is added, which must be done before use, the nitric 

 oxide is expelled, leaving the acid without either increase or di- 

 minution of solvent power : if then we use equal weights of con- 

 centrated pale and red acid, the former will be the stronger. We 

 think we can also defy Mr. Reid to point out a single process, in 

 which the coloured acid is to be preferred to the pale : we know 



that 



