162 Description of a AW Safefif-Pisfon 



seven gros and three grains of s&lt, which exhibited the same 

 phaenomena as muriate of barvtes. 



It appears to result from these experiments, that in eva- 

 porating a mixture of a soKition of muriate of barvtes and 

 phosphoric acid, towards the end of the process, when the 

 sahnc mass ah'cadv formed is capable of bearing a greater 

 degree of heat than that of boiling water, some muriate ot" 

 barvtes is decomposed, which can combine with a part of 

 the free phosphoric acid. 



But that no proper decomposition of the muriate of 

 barvtes takes place by the action of the phosphoric acid, 

 seems to be proved by the large quantity of undecomposed 

 salt and pure phosphorikc acid which was again obtained. 



I sliall abstain from any further inquiry why Morveaii 

 and Gren obtained a precipitate by combining this salt with 

 phosphoric acid ; but I think I can on good grounds con- 

 clude, that neither of these chemists made their experi- 

 ments with pure phosphoric acid. 



X'XV. Description of a New Safety-Piston for Papin's 

 Digester, with tlie Application of it to the Boilers of 

 Sfeam-Ensrines, and also of an Apparatus for regulating 

 the Heat (f Furnaces. By A. N. Edelcrantz, Knight 

 of' the Sivcdish Order of the Polar Star, and Memler of 

 several Academics and. Learned Sncieties,. 



To Mr. Tilloch. 

 SIK7 



XXGKEEABLV lo vour cksire, I havcscnt you the description 

 of a safety -piston which I have employed in Papin's di- 

 gesters; the use of which I have endeavoured to' render 

 inore exact^ safer, and more convenient*. This small ap- 

 paratus, attached to the cover of the digester, consists of a 

 brass cylinder a l<, fig. 2. (Plate III.) in which a piston of 

 the same metal, c d, moves with very little friction, in order 

 that it may descend by its own weight after it has been 

 raised up, without however permitting the vapour to pass 

 between it and the cylinder, llie Ictwer part of the cylin- 

 der communicates with the digester, and is covered by a 

 ?mall sphere, s,s, perforated with holes, to prevent the 

 matters in a state of ebullition from entering the in- 



** The descr'ption of my piston mny be <:ecn in the yaurnn! Jf 

 Pb\si'iiie,\o\. \\\. p. 14.7 But since that time 1 have made snnic change 



in v.i eoiibtruction. 



side 



