328 rHlLOSOTHICAL TRANSACTIONS. [ANNO 1783. 



an aerial form, I next endeavoured to find how much of these acids was taken 

 up at the point of saturation by each 'of the metallic substances, and for this 

 purpose procured the most saturated solution possible of each metallic substance 

 soluble in any of these acids. These solutions did not indeed immediately 

 answer my purpose, as they constantly retained an excess of acid; yet as they 

 were the foundation of my subsequent observations, and as the experiments 

 themselves are in many respects useful to be known, I shall here briefly relate 

 their result, and confine myself to those circumstances singly that relate to my 

 future investigations, or that have not heretofore been satisfactorily explained. The 

 acids I used were dephlogisticated so far as to be colourless; the metals were 

 for the most part verj fine filings, or reduced in a mortar to a fine powder. 

 They were added little by little to their respective menstruums, much more 

 being thus dissolved than if the whole was thrown in at once; and the solution 

 was performed in glass phials with bent tubes. 



Solution of iron in the vitriolic acid. — 100 grs. of bar-iron, in the tempera- 

 ture of 56°, require for their solution, lQOgrs. of real acid, whose proportion 

 to that of the water with which it should be diluted, is as 1 to 8, 10, or 12. 

 It would act on iron, though its proportion were greater or lesser, but not so 

 vigorously. If towards the end a heat of 200° were applied, 123 grs. of real 

 acid would be sufficient. The air produced by this solution is entirely inflam- 

 mable, and generally amounts to 155 cubic inches. 



100 grs. of the vitriol crystallized contain 25 of iron, 20 of real acid, and 

 55 of water. When calcined nearly to redness these crystals lose about 40 of 

 water. 



Iron in the nitrous acid. — 100 grs. of iron, to be perfectly dissolved, and not 

 barely calcined, require 142 grs. of real nitrous acid, so diluted as that its pro- 

 portion to water should be as 1 to 13 or 14; and when this last proportion is 

 used, the heat of a candle may be applied for a few seconds, and the access of 

 common air prevented. In this case not above 18 cubic inches of nitrous air 

 are produced, all the rest is absorbed by the solution, and no red vapours appear. 

 But if the proportion of acid and water be as 1 to 8 or 10, and heat be applied, 

 a much greater quantity of iron will be dephlogisticated, though very little of it 

 be held in solution; and by this means I have obtained from 100 grs. of iron 

 83.87 cubic inches of nitrous air; and by distilling the solution a still greater 

 quantity may be obtained, which was absorbed by the solution. 



Iron in the marine acid. — 100 grs. of iron require 215 of real marine acid for 

 their solution. The proportion of acid to that of water in the spirit of salt I 

 used was as l to 4. When it is as l lo 5, it effervesces too violently. Heat is 

 rather prejudicial, as it volatilizes the acid. No marine air flies off, and the 

 quantity of inflammable air is just the same as if dilute vitriolic acid were used. 



