VOL. LXXVIII.] PHILOSOPHICAL TRANSACTIONS. 4/3 



XIX. Additional Experiments and Observations relating to the Principle of 

 Acidity J the Decomposition of Water, and Phlogiston. By Joseph Priestley , 

 LL.D., F.R.S. p. 313. 



When Dr. P. wrote the former paper on this subject, he says he had found 

 that the decomposition of dephlogisticated and inflammable air, by means of 

 the electric spark, produced an acid liquor, which Dr. Withering found to be the 

 nitrous; though it should have been observed, that he expressed some doubt 

 whether the liquor did not also contain some other acid besides the nitrous. 

 Dr. P. has since that time been desirous to ascertain the quantity of acid pro- 

 ducible from a given quantity of air; and with this view he gave Mr. Keir as 

 much of the liquor as he had collected from the decomposition of about 500 

 ounce measures of dephlogisticated air, and the usual proportion of inflammable 

 air mixed with it. The liquor, he informed Dr. P., was 442 grains, of the spe- 

 cific gravity of 1022, that of water being 1000, and that it contained as much 

 acid as was equivalent to 12.54 grains of concentrated acid of vitriol; which 

 quantity of vitriolic acid is capable of saturating as much vegetable fixed alkali 

 as is contained in 224- gi*ains of dry nitre, or about 23^ grains of nitre crystal- 

 lized in mean temperature. The sediment of the same liquor he also sup- 

 posed to contain, at least, as much acid as the liquor itself. From the preceding 

 data, given by Mr. Keir, and making allowance for the indefinite quantity of 

 water contained in the concentrated acid of vitriol. Dr. P. thinks that not much 

 more than a 20th part of dephlogisticated air is the acidifying principle, and that 

 1 9 parts are water. 



Though Mr. Keir found the greatest part of the acid in the liquor with which 

 Dr. P. furnished him to be the nitrous, there were evident signs of its contain- 

 ing a small portion of marine acid, by its making a precipitation with a solution 

 of silver in nitrous acid. But this mixture of marine acid, he observes, is con- 

 stantly found to accompany the production of nitre in the operations of nature. 

 Whether the different substances from which the dephlogisticated air was ex- 

 tracted made any difference in this case, Dr. P. cannot tell; but that which he 

 gave Dr. Withering was from minium, and that which Mr. Keir examined was 

 from manganese. In the notes which Dr. P. took of the first production of this 

 liquor he termed it blue, and Dr. Withering also calls it blue, and once a green- 

 ish blue; but that which he gave Mr. Keir, and all that he got afterwards, was a 

 decided and deep green, which Mr. Keir thinks to be owing to the phlogistica- 

 tion of the nitrous acid. 



That water enters into the constitution of every kind of air Dr. P. supposed, 

 because it certainly does into that of inflammable, fixed, and dephlogisticated 

 air, and because none of them can be produced except by processes in which water 

 either certainly is, or may be well supposed to be present. That nitrous air also 



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