SIO Drs, Will and Fresenius on the 



of the supposed alkaline chlorides and added to that of the 

 magnesia as previously ascertained. The quantity of potash 

 is determined by means of chloride of platinum in the usual 

 way ; and that of the soda is calculated from that of the chloride 

 of sodium, indicated by deducting the weight of the chloride 

 of potassium from that of the mixed alkaline chlorides. 



4. EstimatioH of the Sulphuric and Phosphoric Acids. — From 

 the acidulous solution (c), the sulphuric acid is first separated 

 by means of chloride of barium. The filtered liquid is nearly 

 neutralized with ammonia, acetate of ammonia is added, and 

 then a solution of perchloride of iron, until the liquid begins 

 to turn red, owing to the formation of acetate of iron. Care 

 must here be taken that sufficient acetate of ammonia be added 

 to convert the whole of the chlorine of the perchloride into sal- 

 ammoniac. The solution is now boiled until it is colourless, all 

 the iron being then precipitated. The precipitate, after being 

 washed witlji hot water, consists of phosphates of iron and a 

 quantity of basic acetate of iron. It is dried, ignited in a 

 platinum crucible, treated with a few drops of nitric acid, re- 

 ignited and weighed. It is next digested with concentrated 

 hydrochloric acid, which speedily dissolves it. The solution 

 is diluted with hot water mixed with tartaric acid, and am- 

 monia is added until the yellowish-white precipitate which is 

 at first formed disappears. A clear solution, but of a dingy 

 green colour, is thus obtained, from which the iron is preci- 

 pitated by means of sulphuret of ammonia. The precipitate and 

 supernatant fluid are digested together in a warm place until 

 the latter loses its green tinge and is of a clear yellow colour, 

 resembling that of the sulphuret of ammonia. It is now ra- 

 pidly filtered, access of air being excluded, and the precipitate 

 is washed with hot water containing a little sulphuret of am- 

 monia, until a drop of the filtered liquid, dried upon a pla- 

 tinum spatula and ignited, no longer indicates an acid reaction. 

 The sulphuret of iron is dissolved from the filter by means of 

 hot and dilute hydrochloric acid, the solution is boiled, treated 

 with a few drops of nitric acid to peroxidize the iron, and 

 ammonia is then added in excess. The precipitate is pure 

 peroxide of iron, whose weight, deducted from that of the 

 basic phosphate, gives the quantity of phosphoric acid. It 

 is essential that the perchloride of iron used in this experi- 

 ment be quite free from sulphuric acid. 



5. Estimation of the Chlorine. — A fresh portion of ash (about 

 1 gramme) is weighed out, exhausted by means of hot water 

 slightly acidulated with nitric acid, and the solution is precipi- 

 tated with nitrate of silver. If the ash contain appreciable 

 quantities of iodine or bromine, these bodies will be found in 



