LETTER TO DR. CRELL 259 



vestiges of muriatic acid. When the author comes to 

 examine the precipitate again, he will not fail to recognise 

 it for luna cornea. 



P. 472. Mr. W. has no doubt of the presence of a 

 great quantity of fixed air in nitre. For my part, I 

 entertain many doubts whether fixed air can be obtained 

 from nitre, and still more, from nitrous acid. I have 

 already observed that a great deal of fixed air is procured 

 from charcoal distilled with recently prepared minium ; 

 and the same thing holds when the phlogiston of the 

 charcoal unites with the acid of the nitre. Why is no 

 fixed air obtained when metals are deflagrated with nitre ? 

 In this case corrupted air is obtained, which does not 

 precipitate lime-water. Moreover, only one-sixth part of 

 the air obtained from gunpowder is fixed air ; the rest 

 is corrupted air. 



P. 480. Mr. W. maintains, after Beaume, that calcareous 

 earth may be converted by a very violent fire into a vitri- 

 form earth ; but in this point I can neither give credit 

 to Mr. Beaume nor the author. 



LETTER FROM MR. SCHEELE TO DR. CRELL. 



I have often prepared the colouring neutral salt con- 

 tained in lixivium sanguinis in the following manner : I 

 extract Prussian blue with thoroughly caustic-fixed alkali. 

 To the liquor containing the extract, after it has been 

 filtered, I add highly rectified spirit of wine, upon which the 

 salt falls in the form of flocculi to the bottom. 1 With 



1 Truth obliges me to mention that, three months before I received 

 this letter, Mr. Westrumb described the same experiment for purifying 

 the lixivium sanguinis. I can say nothing further to decide the priority 

 of the discovery. Crell. 



For an account of Mr. Westrumb's method, see the notes on Bergmann's 

 Dissertation on Elective Attractions, p. 337. T. 



