P II o

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(' 209 )

The mixture thickens extremely by handing, fothat if this quantity of water is not fufficient,more muft be added to bring it down to theconfiftence of thick foup. Then pour thewhole mixture on a linen bag, by which theclear liquor will run through, and leave thewhite pulpy mafs on the filter, which muft beftrongly preffed and then waflied with a pint ortwo of boiling water to extract all the acid.Unite all the liquors together, and after theyhave flood a little to become quite clear theyare fit for evaporation. This liquor now con-tains almoft all the phofphoric acid of thebone-afh, chemically united with a portion ofundecompofed phol'phat of lime, and alfo holdingfome fulphat of lime in folution. The whitemafs in the filter is fulphat of lime, which maybe thrown away. The liquor may be eitherboiled down immediately, or as Dr. Higginsrecommends, firft faturated with ammonia andthen evaporated. The former is the commoneftmethod, and where the object is only to procurephofphorus and not pure phofphoric acid, it isprobably preferable. The boiling down of thislarge quantity of acid liquor is tedious. It maybe done either in large Wedgewood-ware eva-porating pans over charcoal, or in a copperpan, as this acid does not readily a£l oncopper. Keep up a brifk heat and continuethe boiling almoft to drynefs, during which theclear liquor as it becomes concentrated will bemuddy from the reparation of felenite, and agreafy looking pafty acid mafs will depofit onthe lides of the vefl'el. When the liquor isboiled down nearly to drynefs, carefully add toit the fcrapings from the fides of the veffel andlet it Hand fome hours that all the felenite maybe precipitated. Then rediffolve the whole inas little cold water as will take up all the acid,filter it off from the felenite, and evaporate ittill it becomes a pafty puffy mafs, which is nowintenfely four and confifts of phofphoric acidholding fome phofphat of lime. Then mix itthoroughly with a fourth of its weight of pow-dered charcoal, and dry the whole in any vefl'el'vith a heat juft below rednefs. It is then fit forthe fubfequent procefs of diftillation.

Dr. Higgins recommends the following ma-n agement of the liquor feparated from the fele-nat C ? lafs 'T hltration : c faturate it with carbo-r ° art imonia, and boil, which will caufe the„ ™ 10n a h the remaining earth; then

till ?r ^ te j^ le c ^ ear hquor in a leaden boilertill it is reduced fo far that

phat ot ammonia will

crvftalsdepofit by

of phof-cooling.

Pour this folution while hot, into a thin glafsballoon, cover the mouth loofely with aninverted pot, and heat the balloon flowly tillthe bottom is obfcurely red. A copious fub-limate arifes, confifting of fulphat of ammonia,with moft of the ammonia by which the phof-phoric acid was neutralized, and the latter acid(not being volatilizable by any heat) remains inthe form of a colourlefs tranfparent glafs,eafily feparable from the veffel by the blow ofa hammer. It is phofphoric acid in greatpurity, containing probably nothing but a littleremaining ammonia. Phis is then powderedin a mortar and thoroughly mixed with abouthalf its weight of charcoal, and is then fitfor diftillation.

The procefs of diftilling phofphoric acid andcharcoal to obtain phofphorus is in itfelf veryfimple, but fome precautions are required inthe management. Phofphoric acid by itfelfvitrifies in a red heat and is not further changedby any intenfity of fire, but when in contactwith any carbonaceous matter it is decompofed,yielding its oxygen to the charcoal, whiift thephofphorus flies off in the form of vapour,which is condenfed when it arrives at a coolerplace and concretes into a brown-red waxymatter. A very ftrong red or red-white heatis required for this purpofe, (probably aboutthe degree fuflicient to melt copper) fo thatthe retort muft be of earthen-ware and fitted toa powerful reverberatory furnace, or furroundedwith burning charcoal in confiderable mafs andheaped up for fome height above its neck.As at this temperature the common crucibleware becomes very porous, much of the vapourof the phofphorus would ooze through (evenwithout any accidental flaws or cracks) fo thatthe retort fliould previoufly be coated witha vitrefcent lute, of which there is none betterthan flacked lime brought to a moderately thinconfiftence by a faturated folution of borax inwater, and brufhed over the outfide of theretort and flowly dried. This when heatedforms a thin glazing which flops up moft ofthe pores of the vefl'el. In the diftillation thecontact of the external air muft be carefullyexcluded, otherwife the phofphorus as foon asformed would take fire and confume fpeedily.This is prevented Amply by elongating the neckof the retort with another earthen or metaltube cemented to it by glue lute , {fee the articleCement ) and dipping the end of the fecond tubeabout an inch in a pan of water. Thus all thegaffeous products pafs through the water, and

c Higgin’i Minutes, p. 1 $

2 D

¥01.. II.