462 NITROUS ACIDS. 



4. Apparent caprice. 



(a.) It has been found, however, that the amount of oxygen ab- 

 sorbed, is very different in different cases, and that it is influenced by 

 the proportion in which the gases are mixed the time that elapses 

 after they are mixed the size and form of the vessels the greater 

 or smaller surface of the water over which, and the rapidity with 

 which, the mixture is made ; and perhaps by other causes, such as 

 agitation, temperature and order of mixture. 



(b.) According to Davy, when large quantities of nitric oxide gas 

 are added to small quantities of oxygen in vessels of large diameter, 

 the absorption is from 2 to 3 of nitric oxide for 1 of oxygen but if 

 large quantities of oxygen are added to small quantities of nitric ox- 

 ide gas in narrow tubes, the absorption is from 1 to 1.5 of oxygen in 

 volume, and 2 of the nitric oxide gas. 



(c.) Surface of water. In general, the larger the surface of the 

 water, the more rapid the absorption and therefore for want of time, 

 less oxygen is combined ; in such case, more of the nitrous and less 

 of the nitric acid will be formed. 



(d.) Cause of the variable absorption. Dr. Priestley, supposing 

 that the nitric oxide and oxygen combined in only one proportion, 

 very early employed them in eudiometry but he was ignorant of the 

 fact that they combine in three proportions ; producing hypo-nitrous, 

 nitrous and nitric acids, and that it is the varying production of one 

 or another of these, and in different proportions, that creates the ap- 

 parent caprice. 



(e.) Can the uncertainty be removed ? Dr. Henry, in his Ele- 

 ments Mr. Dalton, in the 10th Vol. of the Annals of Philosophy, 

 and Gay-Lussac, in the 2d Vol. p. 247, of the Memoires d'Arceuil, 

 have given minute directions how this may be with more or less 

 certainty effected. 



(/.) The process of Gay-Lussac, resembling the original one of 

 Dr. Priestley, is worthy of being mentioned. 



In a wide jar, a common tumbler glass, or a tube not less than 1 J 

 inch in diameter,* add 100 measures of nitric oxide, to 100 of com- 

 mon air ; the absorption will be complete in half a minute or a min- 

 ute ; the residue being measured in a graduated tube, will indicate a 

 diminution of 84 measures out of the 200 ; one fourthf of the di- 

 minution is oxygen, =21, and 8421 = 63, the proportion of nitric 

 oxide gas that has been acidified. 



In applying this process to mixed gases, containing sometimes more 

 and sometimes less than the oxygen in the air, the result was found 

 to be correct. When the proportion of oxygen was greater than in 



* Murray. 



t The division by four seems to be founded on experience only, as no reason ap- 

 pears why that number should give in this case a uniform result. 



