TEST. 



the water wliich fwims at top J and let this walhuig be fo 

 often repeated, that all the moft minute lumps of the clay 

 bo broken, and whatever fait it contains perfeftly vvafhed 

 out : then add to this fine clay, of the pureft fand, of pow- 

 der of calcined flints, ground, and well walhed, of faulty 

 but clean Heffian crucibles, or of any mcombuftible ftoncs 

 ground very line, fuch a quantity as wnll render the mais 

 thick, and hardly adhering to the hands in kneadmg it, or 

 pliant when rolled into a thin lamina. 



This is the matter for making this fort of tefts ; but, be- 

 fore any quantity of the velTels be made of this earth, it will 

 be prudent firft to finilh a fingle one, and try it, by putting 

 on it a quantity of glafs of lead, and expofing it for an hour 

 or more to the ftrongeft fire ; by this trial you will be cer- 

 tain whether or not the mat's is capable of making veflels 

 that will refift both the fire and the glafs of lead ; and by no 

 other means but this trial is it poffible to determine the due 

 proportion of the mixture of the ingredients for this ufe, 

 on account of the variety of the clays. Nature in fome 

 places affords a clay fo well tempered, that it is extremely 

 proper for the making of tefts without any preparation, or 

 without the admixture of any other matter. Sometimes 

 this only requires a (imple walhing, but commonly it is ne- 

 cetrary to make it into balls, and powder or wafh them as 

 before direfted. 



On the trial of a teft made of this, or the former mixed 

 clay, if it runs into glafs, you mull add to it of the powder 

 of Hones, efpecially fuch as beft relifts the fire. Great care 

 is to be taken not to add too much powdered chalk to thele 

 compofitions, fince if the matter is tempered with that 

 alone, the tefts will indeed refift the fire very well, but being 

 too porous, they will yield a paffage to litharge, which will 

 foften them to fuch a degree, that they will either fall afun- 

 der of themfelves, or be totally cruftied when taken hold of 

 with the tongs. 



Thefe veflels are to be made in the following manner : 

 rub over the fides and bottom of a fmall mortar, and alfo 

 its peflle, with oil, or with the fat of bacon ; fill it two- 

 thirds full of prepared clay, then make a (light impi-eflion 

 with your fingers in the middle of the clay ; then place the 

 bottom of the peftle there, and force it down with blows of 

 a hammer, the ftronger the better. When thus properly 

 hollowed, take it out of the mortar, and pare its edges, and 

 dry it, as the coppek are dried, in the air, in a dry warm 

 place. 



Tefts thus prepared may be ufed as foon as dry, unlefs 

 for falts or litharge ; but thefe bodies, when melted in vcffels 

 not firft^ baked or hardened in the fire, always make their 

 way through them. 



Some of the German writers alfo recommend, both for 

 tefts and coppels, a fort of friable opaque ftone, called 

 white fpath, which appears to be a fpecies of gypfum, 

 or of the ftones from which plafter of Paris is prepared. 

 The fpath is direfted to be calcined with a gentle fire, 

 in a covered veffel, till the flight crackling, which happens at 

 firft, has ceafed, and the ftone has fallen in part into powder ; 

 the whole is then reduced into fubtle powder, which is 

 paffed through a fine fieve, and raoiftened with fo much of 

 a weak folution of green vitriol, as is fufficient for making 

 it hold together. Gellert, however, finds, that if the ftone 

 is of the proper kind, which can be known only by trials, 

 calcination is not neceffary. Thefe tefts are liable to foften 

 or fall afunder in the fire, which inconvenience may be 

 remedied, according to Scheffer, by mixing with the uncal- 

 cined ftones fomewhat lefs than equal its weight, as eio-ht- 

 njnths of fuch as had been already ufed and penetrated by 

 the fcoria of the lead, taking that part of the old teft which 



appears of a green-grey colour, and rejefting the red crull 

 on the top. But from his account it appears, that thefe 

 tefts are lefs durable than thofe made of the alhes of bones, 

 though much fuperior to thofe of wood-afties. Vegetable 

 afltes, which Hand pretty well tlie tefting of illver, can 

 fcarcely bear any great quantity of gold, which requires a 

 confiderably ftronger fire than the other ; but bone-aflies, 

 fays Dr. Lewis, anfwer fo effeftually, and are among us fo 

 eafily procured, that it is uiineccflary for the refiner to fearch 

 for any other materials. Cramer's Art of Allaying, p. 6o. 

 62. Lewis's Com. Ph. Tech. p. 144. 



TEST-Z./yuor, a term ufed by our dealers in brandies, &c. 

 for a liquor which they ufe as a teft of brandy, &c. to 

 prove whether they be genuine, or mixed with home fpirit. 

 The people who ule this, place great confidence in it, but 

 it is really a very vague and uncertain thing. They pretend 

 that this liquor will /hew, by the colour which it makes on 

 its being poured into brandy, whether it be genuine or 

 adulterated ; or if not genuine, in what proportion the 

 adulterating fpirit is mixed with it. 



The whole faft is this : if a little common green or white 

 vitriol be diflblved in fome fair water, it makes a teft-liquor, 

 a few drops of which being let fall into a glafs of old French 

 brandy, will turn the whole to a purple or fine violet-colour ; 

 and by the ftrength or palenefs of this colour, the dealers 

 judge the brandy to be genuine or mixed in different propor- 

 tions, with home fpirits. 



Old French brandy, having long lain in the cafk, takes a 

 dilute tinfture of the wood of the cafk, that is, of oak ; and 

 this being of the fame nature with a folution or tincture of 

 galls, naturally turns blueifh or blackifh with vitriol. A 

 new diftilled brandy, though wholly foreign, would not give 

 this teft ; and a common malt fpirit, with oak chips infufed 

 in it, will turn as dark as the fineft brandy. While our 

 diftillers, indeed, had nothing in ufe for the colouring of 

 their fpirits but burnt fugar, it was poffible to make tome 

 guefs at an adulteration with them, becaufe the brandy, in 

 this cafe, would not become blackifh in proportion to its 

 former colour ; the fugar colour not turning to ink with the 

 vitriol, like the other : but our diftillers have fince found 

 a way of ufing an extraft of oak for the colouring of their 

 fpirits, and fince that, this teft-hquor is of very little ufe, 

 our common fpirits, of any kind, turning as deep with it as 

 the foreign brandies. 



The very beft way of making this teft-liquor, is with a 

 c.ilcined vitriol of iron, diffolved in a dilute or aqueous mineral 

 acid. The liquor, when well made in this manner, is of a 

 fine yellow colour, and will give, for a time, the fineft blue 

 to any fpirituous tinfture of oak. 



The EngHfh were, at one time, ver/ fond of high-co- 

 loured brandies, .and it was then that the ufe of this teft- 

 hquor was moft efteemed ; afterwards we, as well as other 

 nations, finding that this colour was only owing to the cadi, 

 began to diflike, and to favour the pale brandies : at length 

 we fell into the ufe of fuch as were wholly limpid and 

 colourlefs, and the re-diftilling of all the old brandies of which 

 people were poffeffed, took place ; on this the teft-liquor was 

 fdund to be of no ufe at all, and accordingly rejefted ; but 

 as we are of late again come into the efteem of coloured 

 brandies, and that with great juftice, as the colour, when 

 genuine, is a certain mark of the age of the liquor, this teft- 

 liquor is again got into more credit than it dcferves. 



The famous Helvetian ftyptic depended wholly on this 

 accident for its colour ; and it was no fmall mortification 

 to our chemifts, when, fome years ago, it was introduced 

 into ufe among us, that they could not make it with our 

 own fpirits, but muft be at the expencc of true French 



brandy 



