NITROUS ACID. 459 



The representative number of hypo-nitrous acid is 38, made up 

 of 1 proportion of nitrogen, 14, and 3 of oxygen, 24 ; thus answer- 

 ing to 1 volume of nitrogen, and l of oxygen 1 volume of oxygen 

 representing two proportions, viz. 16. 



5. The hypo-nitrous acid cannot be obtained from its alkaline 

 combinations in the isolated form, for whenever a stronger acid is 

 added, to separate it from the alkali, it is decomposed into nitrous 

 acid, and nitric oxide gas. 



NITROUS ACID. 



It has been already explained, in what sense this term has been 

 generally used by chemists. It now appears that there is a distinct 

 and peculiar acid, to which the term may be properly applied. 



1. PREPARATION. 



(a.) According to Dr. Thomson* the distillation of dry nitrate 

 of lead into a receiver kept cold by a mixture of snow and salt, affords 

 this acid in purity ; Gay-Lussac considers it as the hypo-nitrous.f 



(b.) Sir Humphry Davy obtained it by mixing in a vessel deprived 

 of air, 2 volumes of nitric oxide and 1 of oxygen, the gases being both 

 dry. The condensation, according to Davy, is into one half; ac- 

 cording to Gay-Lussac and Dr. Thomson, into one third of their 

 original volume. 



(c.) The correct performance of this experiment requires a glass 

 globe adapted to the air pump, and also to glass jars from which 

 the two gases can be introduced in their proper proportions. 



(d.) The common class experiment of mingling the gases by pour- 

 ing them into glass jars through water, in the pneumatic cistern, gives 

 a mixed acid ; composed probably of the three varieties nitric, ni- 

 trous, and hypo-nitrous. 



2. PROPERTIES. 



(a.) In dry glass vessels, it forms a deep blood red vapor, or per- 

 haps it might be called a gas. 



(b.) It is, however, condensed into a liquid by a low temperature. 

 The density of the anhydrous acid is 1.451. 



(c.) We have the authority of Dulong and of Dr. Thomson, that 

 the red fuming acid distilled into a cold receiver from nitrate of lead, 

 is really anhydrous nitrous acid. 



(d.) ItJ is very corrosive intensely acid odor very pungent, 

 color, yellowish orange at common temperatures, it is a fuming li- 

 quid, but evaporates rapidly and boils at 82 Fahr. The exhala- 

 tions are the common nitrous acid vapors, which, when once mingled 

 with other gases, require a very intense cold to condense them. 



* Elements, Vol. I, p. 120. t Ann. de Chira. et de Phys. Vol. I, p. 405. 



i It will be observed that this description applies also to what Gay-Lussac consid- 

 ered as hypo-nitrous acid ; see his memoir, Ann. de Chim. etde Phys. T. I, p. 405. 



Berzelius remarks that nitrous acid of the same density with nitric that boils at 

 236, boils at 160. 



