Reid's " Elements of Practical Chemistry" 453 



that Dr. Hope has already made a similar assertion, but it was un- 

 accompanied by proof, and the Edinburgh Pharmacopoeia certainly 

 does not contain any. 



At page 60 our author states that " nitric acid (by which the com- 

 mon liquid nitric acid is always understood, composed of one equi- 

 valent of real acid and two of water,") possesses certain properties, 

 all of which it is not requisite to quote ; but he tells us that " it is 

 distinguished from all other acids by the facility with which it af- 

 fords oxygen to metals and combustible bodies, most of which de- 

 compose it with great rapidity." This the reader will remember is 

 stated of acid of sp. gr. 1-5 : and yet in direct contradiction to this, 

 and only six lines further on in the same page, we are informed 

 that nitric acid of sp. gr. 1-48 " is scarcely affected by the metals 

 at ordinary temperatures/' requiring the addition of a "small quan- 

 tity of water" to cause its decomposition. Here then occurs another 

 instance of that want of care of which we have given so many} — 

 nitric acid of sp. gr. 1-5, containing of course less water than that 

 of 1*48, is decomposed by metals " with great rapidity;" while that 

 of 1*48, which contains more water than that of 1-50, " is scarcely 

 affected by the metals at ordinary temperatures, without adding a 

 small quantity of water." 



Let us then suppose that the acid is to be diluted; yet when it is 

 decomposed by metals " all the oxygen, however, is not withdrawn 

 from the nitrogen, nitric oxide, and nitrous acid, being generally 

 disengaged during the action that takes place." These statements 

 are, we apprehend, not quite correct : we admit that nitric oxide is 

 usually evolved, and sometimes nitrous oxide is mixed with it; but 

 the nature of the gases depends upon the strength of the acid and 

 the nature of the metal; for zinc and very dilute nitric acid, give 

 nitrous oxide nearly pure and unmixed with nitric oxide ; and we 

 much doubt whether nitrous acid is in any case whatever evolved. 

 Has not Mr. Reid mistaken the production of nitrous acid, by the 

 action of nitric oxide upon the oxygen of the atmosphere, for its 

 direct evolution by the action of the metal ? 



On the subject of the action of dilute nitric acid upon the metals, 

 Mr. Reid has, if we mistake not, committed another error. After 

 stating that the nitric acid and water are both decomposed, he says : 

 " When this takes place, the hydrogen of the water unites with the 

 nitrogen of the acid forming ammonia, which combines with part of 

 the nitric acid that is not decomposed, forming nitrate of am- 

 monia : this explains,'' continues Mr. Reid, " the appearance of the 

 white fumes which are often seen intimately blended with the ni- 

 trous acid vapours that are formed when this acid is decomposed 

 by a metal having a great affinity for oxygen." 



For our part, we must confess that we had never observed this 

 blending of white and red vapours during the solution of a metal ; 

 but Jiat experimentum is our motto, and we accordingly mixed 

 some diluted nitric acid and tin ; and we do admit that for a mo- 

 ment, and by the action of the heat generated before any consi- 

 derable evolution of nitric oxide occurred, that some white vapours 



were 



