508 Drs. Will and Fresenius on the 



paper. This is easily effected if the matters be perfectly dry, 

 the paper in most cases only retaining so much as to be 

 slightly coloured by the charcoal. The powder is now boiled 

 for half an hour with pure potash ley (free from silica), by 

 which the whole of the silica will be gradually dissolved, lea- 

 ving the sand and the charcoal unacted upon. The insoluble 

 matter is again collected on the same filter, washed, and dried 

 atlOO°C. until it no longer loses weight. The increase upon the 

 weight of the dried filter is estimated as charcoal and sand. 



The filtered solution, after the addition of hydrochloric 

 acid in excess, evaporation to dryness, and treatment in the 

 usual way, gives the quantity of silica. 



The acid solution, originally filtered from the silica, sand 

 and charcoal, after being well mixed, is divided into three, or 

 more conveniently into four equal portions, one being reserved 

 in case of misfortune with either of the other quantities. The 

 division is best accomplished by means of an accurately gra- 

 duated tube : the whole of the fluid is collected into the tube, 

 the entire measure then representing the weight of ash experi- 

 mented upon. The solution is now divided into three or four 

 equal or known portions, the volume of each is noted, and 

 they are distinguished by the letters a, h, c and d. 



In [a) the peroxide of iron, oxide of manganese, and the 

 alkaline earths are estimated. 



In {b) the alkalies. 



In (c) the phosphoric and sulphuric acids. 



2. Estimation of the Peroxide of Iron and of the Alkaline 

 Earths. — To the solution (a) ammonia is added until the pre- 

 cipitate which is thereby produced no longer entirely redis- 

 solves ; acetate of ammonia is next added, and sufiicient acetic 

 acid to render the solution strongly acid. From the form 

 and appearance of the precipitate it can easily be judged whe- 

 ther it still contains phosphate of lime ; if this be the case, 

 more acetic acid must be added. The yellowish-white pre- 

 cipitate which remains consists of phosphate of the peroxide 

 of iron, 2Fe2 O3 + 3PO3. Its separation from the fluid is 

 assisted by gently heating it, it is then well washed upon a 

 filter with hot water, ignited and weighed *. 



* We have submitted to careful analysis the white, or rather greenish- 

 yellow precipitate, formed by mixing solutions of the common phosphate 

 of soda and a persalt of iron. The formula of this compound, when dried 

 without heat over sulphuric acid, is 2Fe„ O3 -f SPO^ + 13Aq. Of these 

 13 equivalents of water 6 go off at 100°''C., 4 more at from 300° to 400°, 

 but the remaining 3 are only expelled by strong ignition. The rational 

 formula is therefore 3PO3, 2Fe2 O3, 3H0 + 4H0 + 6Aq. The numbers 

 obtained by analysis were as follow : — 



I. 1'8087 grm. of the substance dried over sulphuric acid lost at 100° C. 

 0-199 water=M00 per cent., and 0-131 more=7-24percent.at300°to400®. 



