NITRIC ACID. 451 



and its constitution, 5 equivalents of oxygen 40, and 1 of nitrogen 

 = 14, its own equivalent being therefore 54.* 



Liquid nitric acid, sp. gr. 1.50, contains 2 proportions of water, 

 18 + 54 = 72 for the representative number. 



Dr. Thomson assigns the sp. gr. 3.75, to the dry gaseous acid, 

 and this number is produced by multiplying .06944, the specific 

 weight of hydrogen, by 54, that of nitric acid. 



5. POLARITY. In the galvanic circuit, this acid is attracted to the 

 positive pole, and is therefore electro-negative. 



C. USES. 



(a.) The nitric acid is a very important agent in chemistry. 

 From its yielding its oxygen with so much facility, it is often em- 

 ployed to oxidate substances of various kinds, and particularly several 

 of the acids are formed in this way. It attacks and decomposes all 

 vegetable and animal substances, giving oxygen to their carbon, to 

 form carbonic acid, and to their hydrogen to form water. 



(b.) It is also much used in the arts ; by engravers in etching 

 their copper plates ; in the solution of metals, and in dyeing ; es- 

 pecially with muriatic acid, to prepare tin as a mordant for cochineal, 

 to produce the scarlet ; and in forming and fixing other fine colors. 

 It is employed in medicine, particularly in liver diseases ; as an auxili- 

 ary in some other cases, both internally and externally, but in the 

 latter case, diluted, so as merely to prick the skin ; as a very valuable 

 remedy in fevers typhus, petechial and malignant ; and as a tonic. 

 It is diluted to such a degree, as to be only agreeably acid, and it may 

 be qualified By sugar and aromatics. 



The diluted nitrous acid of the Edinburgh and Dublin pharmaco- 

 peias, is composed of equal weights of nitrous acid and water. 



(c.) Vapor of nitric acid expelled from nitrate of potassa by sul- 

 phuric acid, is used in fumigations to counteract febrile effluvia ; 

 it appears to possess a good deal of efficacy in that way, and is 

 not inconvenient to the patient, to whose bed side it may be carried 

 without harm ; no heat should however be applied, as it will then 

 emit very suffocating vapors of nitrous acid. Half an ounce of nitre 

 is mixed with 2 drachms of sulphuric acid, and the vapor from this 

 will fill ten cubic feet. For this application, Dr. Carmichael Smith 

 received from the British Parliament, a reward of 5000 pounds ster- 

 ling. 



(d.) It is one of the great acids of commerce. It forms nitrates with 

 the salifiable bases. All its salts are soluble ; it is separated from 

 them all in a state t)f decomposition, by heat, and the bases, ammonia 

 excepted, are left behind. 



* Henry, Vol. I, p. 324; Thomson's First Priii. Vol. I, p. 112; Ann. of Philos. 

 N.S. VIII, 299. 



