T O U 



T O U 



When you have the metals in each of their due propor- 

 tioiis. each being wrapped up in its feparate paper ; put each 

 f.'parately into a new crucible never ufed for any operation, 

 and, adding a little borax, melt them together in a very- 

 quick fire, which muft be well kindled before with bellows ; 

 or, what is yet better, throw them fuddenly into a hot cru- 

 cible, and as foon as they melt, dir them with a dry wooden 

 peg, burnt at the end, and pour them immediately into an 

 ingot. When this is done, wrap up each raafs, when cold, 

 in its own paper again, and weigh them fingly, in a nice 

 balance ; if they ftill weigh a whole mark, they are good ; 

 but if there is any confiderable deficiency m their weight, it 

 is a fign that your fire, having been-too weak, or of too long 

 duration, has confuraed as much copper as is wanting in the 

 weight ; therefore this mafs mull be efteemed ufelefs, and 

 another made in its place in the fame proportion. 



When this is all finifhed, make with the hammer out of each 

 of thefe fmall maffes, a needle, making them a little hot ; then 

 engrave on each of thefe needles the number of h?.lf -ounces it 

 contains, as before niarked on its paper ; that is, upon the 

 nrit Cxteen, upon the fecond fifteen, and fo on ; and then 

 pierce them at one end, and running a filver wire through 

 their eyes, collect them in order according to their different 

 numbers. Thefe are the filver touch-needles, mad; of the 

 different alloys of filver and copper. 



In Holland they make ufe of the mint mark, divided into 

 grains, for the making of their needles. The firil needle 

 made of pure filver is faid to be of twelve pennyweights. 

 The fecond is made of eleven pennyweights, and eighteen 

 grains, by the addition of fix grains of copper. The third 

 is made of eleven pennyweights and twelve grains, by the 

 addition of twelve grains of copper ; and fo on, the pro- 

 portion of filver decreafing always fix grains, that is, one 

 quarter of a pennyweight at a time, and that of the copper 

 being always increafed in the fame proportion, till at lail the 

 ^veight of the filver is reduced to one pennyweight, and that 

 of the copper increafed to eleven pennyweights, which pro- 

 portion conftitutes the lail needle. 



It is needlefs, however, to go through the whole feries of 

 the needles, by fo fmall progreflions to the very laft, for 

 very delicate proportions cannot be very accurately dif- 

 tinguiflied in the operation. 



TovcH-Xeedlij, Gold. Thefe muft be mixed either with 

 filver alone, or with filver and copper varioufly intermixed. 

 This mixture is called allowing or carating, and is deter- 

 mined with a mark divided into twenty-four carats, or weights 

 of two-fixth parts of an ounce. There is nothing to be ob- 

 ferved about the making of thefe needles, befide what has 

 been already faid in regard to the filver needles ; except that 

 the proportions of the weights are determined in another 

 manner. Thei% needles are made according to the following 

 divifion and order ; and they all weigh one mark. 



The firft is entirely of pure gold, or of 24 csrats. 



23 car, 

 23 car, 



22 car. 

 22 car. 

 21 car. 



7. 21 car. 



8. 20 car. 



9. 20 car. 

 10. 19 car. 

 ! 1. l8 car. 



6gr. 



6gr. 

 6gr. 

 6gr. 



' pure gold. ' 



6gr. 



6gr. 

 1 car. 



1 car. 



2 car. 



2 car. 6 gr. 



3 car. 



3 car. 6 gr. 



4 car. 



5 car. 



6 car. 



> pure filver. 



The decrcafe^oes on thus, by whole carats, till the weight 

 of the gold is arrived at one carat, and that of the filver at 



twenty-three ; for after the ninth needle, you cannot make 

 fo exact a dillinclion of the half-carats. 



N. B. The carat is divided into twelve grains. 

 This mixture of the gold and filver is called the white 

 alloy ; but when copper together with filver enters into the 

 mixture of the gold, then it is called a mist alloy. The 

 needles for trial of pieces thus debafed, are made of mixtures 

 analogous to the former, except only that thofe portions, 

 which in the fij-ft cafe were pure filver, here conCft of cop- 

 per and filver mist. Therefore you have a double lerie? : 

 for the mixture is either of two parts of filver cind one c: 

 copper, or of two parts of copper and one of filver. Fc 

 intlance, 



The firft is of pure gold. 



r23 car. 6gr 

 ' 23 car. 



22 car. 6gr 



22 car. 



21 car. 6gr 



21 car. 

 _ 20 car. 6 gr. J 

 and fo on as in the foregoing. 



2 S^- 



4gr- 

 6 gr. 

 8gr. 

 10 gr. 

 I car. 

 I car. 2 gr 



If in this table you take pure copper inftead of pure filver, 

 and filver inftead of copper, this gives you a third feries of 

 golden needles. And you may have a fourth by mixing 

 with gold equal quantities of filver and copper in the fame 

 proportion. Thefe alloys of gold are much in ufe, but 

 workmen may eafily employ a number of other variations, 

 which, compared with thofe already mentioned, will be diU 

 tinguilhed into a thouland different ways by an experienced 

 perfon, fo that it i> neither poffible, nor neceffary to imitate 

 them all. 



But that thefe golden needles may not be too expenfive, ' 

 they may be made much fhorter than thofe of filver, and after- 

 wards foldered to plates of copper, that may be lufSciently 

 long for ufe. 



The ufe of thefe needles is by means of the touch-ftone ; 

 and arifes hence, that every metal when pure muft have its 

 fpecific colour, that diftinguifties it from the reft : but metals 

 being the moft opaque of all known bodies, the fpecific co- 

 lour of every one appears moft diftinftly when you rub it 

 againft a very black hard ftone ; and if the colours of two 

 or more metals are ezpreffed by large lively fpots, made near 

 each other on the fame plane, by rubbing them againft the 

 furface of the ftone, you will by that means eafily difcem 

 their difference, or their hkenefs. 



The ftone adapted to this ufe, and called from its ofEce 

 the touch-ftone, muft have the followng qualities. It mnft 

 be of the deepeft black, left the tindure of the metal fhould 

 be altered by fpurious rays of light (hining among it : it 

 muft be capable of being pretty well poUftied, for when too 

 rough, the colours of the metals rubbed againll it cannot be 

 nearly or regularly diftinguiihed ; and if it is too fmooth, 

 the metals are but faintly, and too flowly abraded or fcraped 

 by it, efpecially when gold is tried. It muft alfo be neither 

 too hard nor too foft. Trip)oli, coal-duft, and tin-a/hes, are- j 

 ufed in rubbing off the thin metalline crufts, and in a fhort 

 time the ftone when very hard is apt to acquire too fmooth 

 a furface ; and when it is too foft it eafily wears, throws off a 

 duft, and contraSs furrows. 



The ftone is made in the form of a quadrangular prifm, I 

 about an inch thick, and two or three inches long. 



If the proper ftone cannot be procured, moderately fmooth 

 pieces cf ilint are the beft fubftitutes ; a.-.d the more they 

 approach in colour to the other the better. 



The 



