380 Chemical Society : Mr. Parnell on the 



This being the case, the soil or mineral is to be treated with hydro- 

 chloric acid, and the iron which the solution contains per-oxidised, 

 the phosphate of protoxide of iron being soluble in acetic acid. 

 Should the muriatic solution contain more phosphoric acid than 

 oxide of iron or alumina, (which seldom is the case, as the latter are 

 usually predominant,) peroxide of irc.^. or alumina is to be added, 

 the solution must also be freed from every trace of silica. The 

 earthy muriates are precipitated with ammonia, after which acetic 

 acid is added, and the whole gently digested. The precipitate will 

 dissolve again, with the exception of the phosphates of peroxide of 

 iron and alumina. When both these ingredients enter into the pre- 

 cipitate, caustic potassa will give the means of ascertaining their 

 respective quantities. 



The solubility of the phosphate of protoxide of iron, and the inso- 

 lubility of the phosphate of peroxide of iron in acetic acid, when 

 freshly precipitated, give an excellent method to separate quantita- 

 tively these two degrees of oxidation. The manipulation is obvious. 



The discovery by Professor Ehrenberg, that the Brighton chalk 

 consists of microscopic shells, is a decided proof of its animal origin, 

 to which may now be added an additional one, viz. the presence of 

 phosphate of lime, which is a usual, although secondary ingredient 

 of the shells of Crustacea?. 



" On the Action of Chromate of Potash on the Protosulphate of 

 Manganese," by Robert Warington, Esq. See Chem. Soc. 



In the course of some experiments on the formation of double 

 salts of chromic acid with various bases depending on the tendency 

 which might arise, from the resulting affinities, to the formation of 

 certain crystallized combinations, the subject of the present brief 

 communication came under my notice. 



On adding a solution of the yellow chromate of potash to one of 

 the protosulphate of manganese, no turbidity or precipitate takes 

 place, but the mixed fluids become of a deep orange red colour, and 

 after a short period the surface is covered with a dark brown crust 

 or film, and the whole of the containing vessel is coated with the 

 same substance ; at times when the solutions are dilute, this deposit 

 assumes a crystalline appearance. If this compound is prepared 

 under the microscope, in the manner described in a former paper, 

 the first effect is the appearance of numerous minute spherical gra- 

 nules of a fine crimson brown colour, which gradually increase in 

 size until about from six to seven 250ths or '025 of an inch in dia- 

 meter ; a number of delicate crystallized spiculse are then observed 

 to start out in radii from their sides ; and when the solutions em- 

 ployed for its production are diluted, fine stellated groups of pris- 

 matic crystals are obtained. When this substance, which has a 

 dark chocolate hue, is examined by a strong transmitted light, it 

 has a rich crimson brown colour : it possesses the following proper- 

 ties : — it is soluble in diluted nitric or sulphuric acids, without 

 residue, yielding an orange-coloured solution ; when acted upon by 

 hydrochloric acid chlorine is evolved, and a brown fluid results, 

 which by the addition of a few drops of alcohol or other deoxidizing 



