6 PHILOSOPHICAL TRANSACTIONS. [aNNO 1724. 



leaving the sediment (i. e. the colour) upon the strainer, from which it is to 

 be scraped off with a wooden spatula into a smaller earthen vessel. Then pour 

 upon it §ij or §iij of spirit of salt, and immediately a most beautiful blue colour 

 will be produced. To this mixture, after it has stood at rest for a night, add 

 a large quantity of rain water, and stir it well with a spatula. When the [blue] 

 matter has settled, let this water be poured off and fresh water be added ; and 

 let this be repeated until the water, with which it is washed, ceases to have any 

 taste. Then empty out the fine blue sediment upon a linen cloth, that the 

 water may drain from it, and dry it by a gentle heat, for use. 



N. B. It is of great consequence in the preparation of this blue colour, to 

 regulate the calcination of the blood with the salt of tartar properly; beginning 

 with a gentle, proceeding to a moderate, and ending with a strong heat. 



The lixivia should be mixed together as hot as possible, all at once, and with 

 the utmost expedition. 



Observations and Experiments on the foregoing Preparation. By Mr. John 

 Broivn, Chemist, F. R. S. N°381, p. \7 . 



Dr. Woodward having lately communicated a paper to the R. S. containing a 

 process for making the Prussian blue ; Mr. Brown went through it exactly, 

 according to the proportions there prescribed ; and observed, that by a calcina- 

 tion of § 4 of blood dried, with ^ 4 of sal tartari, in 2 hours time that part of 

 the operation was over, and a black spongy substance remained in the crucible 

 weighing §4, a solution of whicii being made in boiling water, and afterwards 

 filtered, the remainder, when dried, weighed 9 draclnns, avoirdupois, the for- 

 mer having been weighed by the same kind of weight. 



The loss in the solution and filtration of the vitriol and alum, is nut worth 

 noticing, having both been very clean before they were dissolved. The mixtures 

 being made as prescribed, with the addition of the sp. salis, the product was a 

 very fine blue, which when well edulcorated by frequent washings, and after 

 that thoroughly dried, weighed § 1, or a little more, and entirely answered the 

 character the author gave of it. 



Among the several experiments made with these liquors, the solution of 

 vitriol, the solution of alum, and the spirit of salt, though they always pro 

 duced a blue, yet that blue differed in degrees of colour, according to the varied 

 proportions of the vitriol and alum, and the colours produced from these several 

 propositions, were each of them improved by the addition of the sp. salis. 



The differences in colour, arising from the several proportions of the vitriol 

 and alum, confirm the truth of the author's prescript, as being the most exact 



