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nefs by long keeping, which fhould be in acovered pan in a cool cellar. When wanted, itregains fufficient ductility merely by beingbeaten for a minute or two, or by the help of afew drops more of the oil. Good glaziersputty, which is made of chalk beat up with dry-ing linfeed oil, much refembles the fat lute inquality.

Another fpecies of lute is that which is com-monly applied round glafs retorts when diftilla-tion with a full red heat is wanted to protectthem from the fudden a£tion of the fire, and togive them firmnefs, and enable them to bearthis heat without flattening or falling togetherwhen red-hot, or melting with the fuel. Aglafs veflel fo prepared with a thick earthencoating may be confidered as an earthen veflelglazed on the infide. The fubftance ufed is amixture of fand with juft fufEcient clay tomake it adhere together, beat up with fomekind of fibrous matter fo as mechanically to en-creafe the tenacity. A natural earthy mixtureof the kind is Windfor loam, or an equally goodone may be formed with coarfe fand and clayor better with fragments of pottery coarfelyground (the fine part being feparated by fiftingand rejected) mixed with more or lefs clay ac-cording to the quality, fo that it will juft mouldtogether when wet. For the fibrous matter, fomeufe horfe-dung, which appears the beft, others,chopped ftraw or chaff, others, chopped horfeand cow hair or tow, all of which anfwer thefame purpofe. A fmall quantity of thefe willfuffice. Beaume recommends about an ounce ofcow’s hair to five pounds of the earthy mixture.A good deal of water fhould be added when thematerials are mixed, and much manual labour isrequired to diffufe the hair equally through themixture. To apply it to a glafs veflel, a retort,for example, take a fufficient quantity of thelute, fpread it out flat on a table, lay the bottomof the retort on the middle of the mafs, and thenturn up the edges of the flat cake, and bring itover the reft of the glafs, preffing it down withthe fingers till it applies uniformly and clofely.By this method the lute is without feam, and ismuch more likely to dry in the fire withoutcracking. Or elfe, bring the lute with fufficientwater to the confiftence of thick foup, dip theretort in, and it will come out thinly coated.Turn it round before the fire, and when dry dipit again in the lute to give a fecond coating, andfo on to the required thicknefs, which may befrom to an inch. A lute fimilar to this is

ufed as a lining to iron furnaces to confine thefire and prevent the iron from confuming by theconftant heat. This lute is juft fo fufible as tobegin to agglutinate in a full red heat, andhence, if it remains found till thus hot, it willform an impenetrable coating to the glafs within,from which it cannot afterwards be detached.The covers of crucibles and other veflels in-tended to bear fire may be luted with this earthymixture. It is rendered ftill lefs liable to crackon the firft heating, if, when thoroughly dry, itis fmeared with linfeed oil.

Sometimes however a ftill more fufible com-pound is wanted, particularly where very vola-tile and penetrating fubftances are diftilledfrom an earthen veflel. Thefe veflels are necef-farily porous to a certain degree, independent ofany cafual cracks, from which the larger earthenveflels are feldom entirely free. When phof-phorus (for example) is prepared by ftronglyheating charcoal and phofphoric acid in one ofthefe retorts, the vapour of the phofphoruspenetrates through the pores when thoroughlyred hot, and much of it is loft. Nor will thelaft-mentioned luting entirely prevent this, fothat it is a great faving to cover the retort firftwith a thin coat of a fufible glazing, which willmelt on the furface as foon as red-hot, andclofe every opening. This glazing may bemade by a variety of fluxes added to the properdofe of clay and earth, and mixed into a thinpafte, and applied to the retort with a brufh.The following management is recommended byMr. Willis/ a practical chemift, in diftillationwith large earthen retorts. Diflolve one ounceof borax in half a pint of boiling water, and addas much flacked lime as will make it into athin pafte. Spread it over the retort with abrufli, and when dry apply over the whole alute of flacked lime and linfeed oil beaten till itis perfectly plaftic. This becomes dry in a dayor two, and is then fit for ufe. Stone retorts maythus be ufed feveral. times with fafety (alwaysrenewing the oil and lime lute) whereas in thecommon way, and even with the clay and hairlute they generally crack when cooling, or onbeing heated a fecond time. If during the ope-ration, the retort fhould crack, Mr. W. advifesto fpread fome of the oil compofition thickly onthe part, and fprinkle fome flacked lime overthe whole, which will prevent the further efcapeeven of the penetrating vapour of phofphorus,and may be fafely applied even when the retortis red-hot. When prepared fomewhat thicker

* Repertory, vol. i.

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