FEL

FE L

( 429 )

made for the inevitable errors to whi(;h themoil accurate analyfis is neceffarily fubject.

The method employed by Vauquelin was thefollowing. c Having fufed the felfpar withcauftic potafh, he diffolved the mafs in dilutemuriatic acid, and evaporated the whole to dry-nefs : r. the faliue refidue being drenched withwater and filtered, the filex remained behindas a white ini'oluble powder. 2. The clearliquor being treated with ammonia produceda copious white precipitate. 3. This precipitatewas digefted in cauftic potafli and left behindthe iron: muriatic acid was then added to fatu-ration, and afterwards carbonat of potalh threwdown the alumine. 4. The liquor No. 2, gaveno precipitate with carbonated potafli or ful-phuric acid, but oxalic acid occafioned a preci-pitate of oxalat of lime, which when dalcined,was confidered as carbonat of lime, whence theamount of the lime was eftimated according tothe ufual proportions. The only exceptionablepart of this analyfis relates to the method ofprocuring the lime* and this on two accounts:in the firft place, oxalic acid would not feparatethe whole of the lime from the liquor, whichconfifted of the muriats of lime, potafli, andammonia; and in the fecond place, the oxalat oflime which was precipitated ought by no means,after having undergone calcination, to be con-fidered as carbonat of lime, but as lime in afemi-cauftic flate. It is further a Angular cir-cumftance and contrary to general experience,that carbonat of potalh Ihould have been unableto throw down the lime from the folution whichwas decompofable by oxalic acid. But evenif we allow the utmoft poffible weight to thefeobjedtions, and in confequence raife the amountof lime in Vauquelin’s analyfis to an equalitywith that of Chenevix’s, there flill remains adifference of 11 per cent, unnaccounted for.That potafli is really contained in the Siberianfelfpar appears alfo from a fubfequent analyfisby Vauquelin , in which he ufed cauftic foda asthe primary l'olvent, and afterwards obtainedcryftals of alum by the addition of fulphuricacid. It is however worthy of notice that theaccount of Vauquelin ’s experiments is not writ-ten by this eminent chemift himfelf, but is con-tained in a paper read at the Societe philomathiqueby Le Lievre, and in confequence is not in theill oft authentic form.

With regard to the oppofite analyfes of adu-laria by the above mentioned chemifts, it is diffi-cult to form any fatisfadtory opinion, as thedetails of Vauquelin ’s'analyfis are not pubfiflied.

* Joura. des Mines, No, 49. p. 24. i Nouymux

It may however be remarked that m the amountof filex they exactly correfpond, and that theproportion of alumine as^ determined by Vauque-lin , approaches much nearer to the ftatementof Chenevix than in the former inftance. Thechief difference is the proportion of lime, butif, as is probable, the fame method was ufed byVauquelin on this occafion as was pradtifed byhim on the former one, it may be fufpedte.dthat Mr. Chenevix’s eftimate approaches nearerto the truth. The water of cryftallizationamounting to 1.75 according to Chenevix, iswholly negledted by Vauquelin -, and it isobvious that the proportion of potafli as givenby this chemift is from mere eftimation, and isreckoned at 14- becaufe juft fo much waswanted to compleat the original 100 parts thathe operated on. The iron obtained by Chene-vix is perhaps only a cafual ingredient of adu-laria: fo that making the requifite allowancesfor each analyfis, the quantity of potafli canhardly be eftimated at more than 6 per cent.It is however greatly to be wiflied that Klap-roth or Hatchett would undertake anew the fullanalyfis of this important mineral in all itsvarieties and fubfpecies.

Some further interefting particulars refpeef-ing felfpar are contained in a memoir by M.Gerhard/ 1 Common felfpar when heated toincandefcence lofes 1 per cent, (probably water).After being calcined it is readily adted on byfulphuric acid, and the product is a little feleniteand much alum ; the filex remaining unalteredby the acid. From an analyfis conducted inthis manner M. Gerhard ftates the conftituentparts of felfpar at

Silex - 64.

Lime - 6

Alumine 30

100

Here it is worthy of remark that the pre-*fence of potafh in this mineral is fully alcer-tained by the copious produdtion of alum whenit is treated after calcination with fulphuric acid,and this is the lefs liable to fufpicion as thememoir was publifhed long before the necef-fity of potafli to the cryftallization of alum wasfufpedted; in confequence of which we findin Mr. G’s analyfis no mention of potafh, andperhaps it is fomewhat in favour of the reduc-tion which we have made in the proportion ofalkali as given by Vauquelin , that this reducedproportion, viz. 6 per cent, added to the quan-Memoires de l’Acad. Roy. do Berlin, for 1783. p. nj.