190 Dr. Hope^s Remarks on Mr, Philiips^$ 4^mlysis [Ma rch, 



qnce here state), which causes a partial decomposition ; but it 

 is altogether a mistake to suppose that the red colour of the acid 

 got by decomposing nitre proceeds from this source. Hundreds 

 pf chemists, 1 presume, as well as myself, have, since the days 

 of Glauber, been in the habit of employing purified nitre, and 

 liave obtained a red coloured acid. It must surely have escaped 

 your memory that the red coloured acid is the spiritus nitri 

 Jumatis, or Glauber's spirit of nitre, the only form of the concejor 

 trated acid familiar to chemists till about 40 years ago. 



In the commencement of the distillation, the acid is pale, aad 

 continues so till towards the close ; tlien, provided the tempera- 

 ture has been raised to the due pitch, it acquires the orange 

 tinge by absorbing the ruddy fumes which now appear accom- 

 panied with oxygen gas proceeding from the partial decomposi- 

 tion of part of the acid. 



As you state that you cannot see why the Edinburgh College 

 should employ the particular proportions directed by them, i 

 beg leave to mention the reasons ; first, the prescribed quantity 

 of sulphuric acid is required, and proves sufficient to detach the 

 whole of the acid from the nitre ; secondly, the acid thus pro- 

 cured is of great strength, and is so free from sulphuric acid, as 

 to render the second distillation enjoined by the London College 

 altogether unnecessary for ordinary purposes. 



Acidum Niiricum. — The criticism of this article appears to me 

 jto be incorrect in every point. Having this moment called your 

 attention to the mistake in regard to the colour and quantity of 

 the acid, I need not recur to them. Though for many purposes 

 the nitric and nitrous acids may be used indiscriminately, yet 

 xhere are some where they cannot with propriety; and the 

 .object of the formula is, to direct the apothecary how he can. 

 .procure a colourless acid ; while at the same time he obtains 

 a portion of the acid in its most nitrous condition. I presume it 

 is from your never having seen the red acid got by our process 

 that you have been led to remark that the red acid when diluted 

 is quite pale ; whereas, in truth, if it be diluted as directed by 

 the Pharmacopoeia, it is of a rich green colour. By free expo- 

 sure indeed to the air, this colour grs^dually, but very slowly, 

 disappears. 



You have assigned as a reason for preferring the process of 

 the London College, should a pale acid be wanted, that it affords 

 it by one operation, while that of the Edinburgh requires two. 

 But you have forgotten that the London Pharmacopceia direcj^s 

 a second distillation of a fresh quantity of nitre, and after all 

 (does not procure a colourless acid. 



Aqua Potasscc. — You object to our process, because thrice as 

 much lime is used as the theoretical quantity ; and because the 

 excess occasions waste by the quantity of the solution retained. 

 Experimentally I have found by many trials, that this excess of 

 Ume deprives the potassa much more cpinpletely of its carbonic 



