606 PHILOSOPHICAL TRANSACTIONS. [aNNO I789. 



quantity which is produced when heated in dephlogisticated air. Prussian blue is 

 generally said to be a calx of iron supersaturated with phlogiston, though of late 

 it has been said by some that it has acquired something that is of the nature of 

 an acid. From his experiments on it, with a burning lens in dephlogisticated 

 air, he infers that the former hypothesis is true, except that the substance con- 

 tains some fixed air, which is no doubt an acid; for much of the dephlogisticated 

 air disappears, just as in the preceding similar process with iron. 



He threw the focus of the burning lens on 2 dwt. 5 gr. of Prussian blue in a 

 vessel of dephlogisticated air, of the standard of 0.53, till all the colour was dis- 

 charged. Being then weighed, it was 1 dwt. 2 gr. In this process 74- oz. of 

 fixed air had been produced, and what remained of the air was of the standard 

 of 0.94. Heating the brown powder to which the Prussian blue was reduced in 

 this experiment in inflammable air, it imbibed 8^ oz. m. of it, and became of a 

 black colour; but it was neither attracted by the magnet, nor was it soluble in 

 oil of vitriol and water, as he had expected it would have been. Again, he heated 

 Prussian blue in dephlogisticated air, of the standard of 0.-2, without producing 

 any sensible increase of its bulk, when he found 3 oz. measures of it to be fixed 

 air, and the standard of the residuum, with 2 measures of nitrous air, was 1.35. 

 The substance had lost 1 1 gr., the greatest part of which was evidently water. 

 To determine what quantity of fixed air Prussian blue would yield by mere heat, 

 he put half an ounce of it into an earthen tube, and got from it 56 oz. m. of 

 air, of which 16 oz. m. were fixed air, in the proportion of -^ in the first portion, 

 and i- in the last. The remainder was inflammable. There remained 5 dwt. 20 

 gr. of a black powder, with a very little of it (probably the surface) brown. 



Comparing these experiments, it will appear, that the fixed air procured by 

 means of Prussian blue and dephlogisticated air, must have been formed by phlo- 

 giston from the Prussian blue and the dephlogisticated air in the vessel: for if 

 240 gr. of this substance yield 16 oz. measures of fixed air, 10 gr. of it, which 

 is more than was used in the experiment, would have yielded only 0.6 oz. m. 

 Nor is it possible to account for the disappearing of so much dephlogisticated air, 

 but on the supposition of its being employed in forming this fixed air. 



XX IJ^. On the Production of Nitrous Acid and Nitrous Air. By the Rev. Isaac 

 Milner, B. D., F. R. S., &c. p. 300. 

 1 . It has been known for some time, that a relation subsists between nitrous 

 acid and volatile alkali. The latter has frequently been produced by help of the 

 former; but Mr. M. does not recollect that, in any instance, the volatile alkali 

 has been proved to contribute to the formation of nitrous acid or nitrous air. 

 Some cases however have occurred where this evidently happens; and they ap- 

 pear so new and extraordinary, that he cannot but think they deserve the at- 



