ANALYSIS. 



libceous. If it remains thick and opaque, the other earths 

 are moil abundaat. If it affumes the form of a pulverulent 

 bulky white powder, the ftone is moftly argillaceous. If 

 the colour be dull green or brownirti, oxyd of iron is pre- 

 fent. A bright grafs-grcen indicates the prefence of man- 

 ganefe, and yellowi(h -green chrome. When a ftone is 

 aluminous and very hard, potalh aAs very feebly upon it ; 

 and in this cafe, borax was ufed with great advantage by 

 Mr. Chenevix. 



The crucible being now removed from the fire, and 

 cleaned externally, is to be placed in a porcelain capfule, and 

 filled with water ; and this is to be repeated till the whole of 

 the matter is feparated. A portion of the compound of 

 potaih, with the filex and alumina of the mineral, is taken 

 up by the water, which wovild indeed diflblve the whole 

 if added in fuificient quantity. 



The detached matter is then to be diflblved in muriatic 

 acid : at the commencement of the folution, an abundant 

 precipitation takes place of a flocculent matter, which had 

 been held in folution by the alkali, with which the acid 

 combines. Then an effervefcence takes place from the de- 

 compofition of the^ alkaline carbonate formed after and 

 during the fufion, and at the fame time the precipitate is re- 

 difTolved. The portion of matter alfo not dilTolved by the 

 water, and which had remained at the bottom in the form of 

 a powder, is dilTolved ; this not being attended with any 

 effervefcence, if it be alumina or filex ; but if it contains 

 Lme, an effervefcence takes place. If the muriatic folution 

 be colourlefs, we may conclude that it contains very little or 

 no metallic oxyd. If its colour be pui plifh-red, it is a 

 further proof that manganefe is prefent ; orange-red indi- 

 cates iron ; and golden-yellow, chrome. 



This folution is now to be evaporated to drynefs upon a 

 fand-bath, in a flat porcelain vefiel loofely covered with 

 paper. Towards the end of the operation, the fluid becomes 

 gelatinous, and requires to be'conftantly ftirred with a filver 

 or porcelain rod, to facilitate the difengagement of the water 

 and acid, and to render the exficcation uniform throughout 

 the whole. If this precaution be not obferved, there is a 

 rifle of a portion of the alumina, from which the acid has 

 been expelled, remaining with the filex ; and with the alumina 

 of a portion of filex being retained in folution ; by the acid 

 on account of its not being fufficiently diffipated. 



When the matter is almoil reduced to the form of a drv 

 powder, a large quantity of diftilled water is to be poured 

 upon it ; the whole is then to be gently heated, and thrown 

 upon a filtre. The powder remaining on the filtre is to be 

 walhed «nth water, until the lafl; portions added give no 

 precipitate with folution of filver. This powder is Jthx. 

 It is to be carefully dried between folds of blotting paper, 

 expofed afterwards to a red heat, and weighed while warm. 

 It ought to be a fine white powder, infoluble in acids. 

 If it be coloured, the prefence of a metalhc oxyd is indi- 

 cated, which is a proof that the heat towards the end of the 

 evaporation had been raifed too high. To remove this oxyd, 

 the powder is to be boiled vnxh an acid, and afterwards 

 waftied and dried, and the liquor muft be added to the 

 filtered fluid above-mentioned. 



The folution is then to be evaporated till its quantity does 

 not exceed an Englilh pint. A folution of carbonate of 

 potalh is to be poured in, till no farther precipitation 

 takes place ; and in order to render the feparation more 

 complete, the whole fliould be boiled for a few minutes. 

 AVhen all the precipitate has coUe<3:ed at the bottom, 

 the fupematant liquor is to be decanted off; and water 

 being fubllituted in its place, the precipitate and water are 

 to be thrown upon a filtre. When the water has paffed 



through, the filtre with the precipitate upon it is to be 

 placed upon fome folds of bibulous paper ; and when the 

 precipitate has acquired a httle confiilence, it is to be care- 

 fully collefted with an ivory knife, and mixed with a folu- 

 tion of pure potath, and boiled in a porcelain crucible. If 

 any alumina or glucina be prefent, they will be diflblved in 

 the potafli, while the other fubftances remain untouched in 

 the form of a powder. 



The folution of alumina in the potafh is to be fuper- 

 faturated with an acid, that is, fo much acid is to be added 

 as is fufficient to rediflblve any precipitate that may be 

 formed. Carbonate of ammonia is then to be added in 

 excefs, fo as to be fenfible to the fmell. This will precipi- 

 tate completely the alumina, if any be prefent, while the 

 glucina will remain in folution. The alumina is to be col- 

 lected on a filtre, wafned with diftilled water, and then dried 

 at a red heat, and weighed. To determine if it be really 

 alumijia, diflblve it in fulphuric acid, and add a fufficient 

 quantity of fulphate or acetate of potafli ; if it be alumina, 

 the whole of it will be converted into cryftals of alum. If 

 glucina be prefent in the remaining liquor, it will fall down 

 on boiling it for fome time, fo as to diflipate the excefs of 

 ammonia. After being wafhed and dried as before, it is to 

 be accurately weighed. 



The matter remaining undiflblved by the folution of 

 potafli above-mentioned may confiil ot lime, magnefia, 

 yttria, and the metallic oxyds. If yttria be fufpefted, add 

 carbonate of ammonia, which will diflblve the yttria, and 

 leave the other bodies. Then let the whole be diflblved in 

 dilute fulphuric acid, and the iolution be afterwards evaporated 

 to drynefs, fo as to difTipate any excefs of acid. A little 

 water is to be added to the foUd refiduum, which will take up 

 the metallic fulphates and the fulphate of magnefia, but 

 leave the fulphate of lime, which is to be dried at a red heat, 

 and weighed ; and from its weight the quantity of lime prefent 

 may be readily eftimated. The fubftances retained in folution 

 by the fulphuric acid may be magnefia and the oxyds of iron, 

 manganefe, chrome, and nickel. To feparate thefe, the 

 folution is to be diluted with a large quantity of water, a 

 flight excefs of acid added to it ; and then a folution of car- 

 bonate of potafli faturated with carbonic acid is to be poured 

 in. The oxyds of iron, chrome, and nickel, will be pre- 

 cipitated, while the magnefia and manganefe will remain 

 in folution v/ith the carbonic acid. To feparate thefe, 

 hydro-fulphuret of potafli well faturated with fulphuretted 

 hydrogen is to be added to the folution, which will precipi- 

 tate the manganefe in the ftate of hydro-fulphuret, while the 

 magnefia will ftill remain in folution. The magnefia may 

 then be feparated by a folution of pure potafli, and its weight 

 eftimated after it is waftied and dried at a red heat. To 

 obtain the weight of the oxyd of manganefe, its precipitate 

 muft be calcined with the admiflion of air to expel the ful- 

 phuretted hydrogen. 



There ftill remain to be feparated the oxyds of chrome, 

 iron, and nickel. To do this, the precipitate is boiled in 

 fucceflSve portions of nitric acid, to bring the oxyd of 

 chrome to the ftate of acid. It is then heated for a few 

 feconds with potafti, and after being heated the liquid is 

 poured off. The undiflblved matters are to be waftied with 

 water, which wafliings are to be added to the other liquid. 

 The chromic acid remains in folution combined with tlie 

 potafti ; muriatic acid is added to it, fo as to be in excefs ; 

 it is then evaporated until it afl^umes a green colour. If 

 pure potafti be then added, the oxyd will be precipitated, 

 and it may thus be collefted, and its quantity afcertained. 



The undiflblved matter of the preceding experiment may 

 confift of the oxyds of iron and nickel. To feparate them, 



they 



