r u R 



The method of obtaining the colour, Mr. Cole (fee 

 VvRVhV.-Fi/h) defcribes thus : 



The (hell, which is very hard, being broken, (with the 

 mouth of the lifh downwards, fo as not to crulh the body,) 

 and the broken pieces being picked off, there appears a 

 white vein lying tranfverfely in a little furrow or ckft next 

 the head of the fidi. 



lu this vein is the purple matter lodged ; fome of which, 

 being laid on linen, appears at firft of a light green colour ; 

 and.^if expofed to the fun, foon changes into a deep green, 

 and in a few minutes, into a fea-green, and, in a few more, 

 into a blue ; thence it foon becomes of a purplifli-red, and, 

 in an hour more, of a deep purple red. 



And here the fun's aftion terminates ; but by wafhing in 

 fcalding water and foap, and drying it, the colour ripens 

 to a moil bright and beautiful crimfon, which will bear 

 ■wafhing admirably without the addition of any ilyptic. 

 While the cloth marked with this colour lies in the fun, it 

 will yield a very ftrong and foetid fmell, as if garlic and affa 

 foetida were mixed together. 



The juice which gives this beautiful purple colour is, 

 fays M. du Hamel, while it remains in the body of the 

 animal, and while that is in health, vvlioUy white ; but no 

 fooner is it expofed to the fun, than it begins to change 

 colour, and in lefs than five minutes goes through the fe- 

 veral changes of pale green, yellowirti, and a beautiful 

 emerald green ; after this it becomes of a deeper and duflcier 

 green, then blueifli, reddidi, and finally a deep and very 

 beautiful purple. Sometimes the juice is found naturally 

 green in the animal : this is probably from the creature's 

 being in a difcafed ftate. But when it is naturally thus, it 

 immediately becomes red, and afterwards purple, on being 

 expofed to the fun ; its feveral preceding changes feeming 

 to have been made already in the body of the animal. 



If a piece of linen be rubbed over with this juice, and 

 part of it expofed to the fun, part not, that only will turn 

 red which is fo expofed, the other remaining green without 

 any alteration ; and it is obferved, that the itronger the fun 

 fhines, the quicker the change appears, and probably the 

 colour is in proportion alfo the more beautiful and hvely. 

 And it is very remarkable, that if a needle, or any other 

 opaque body, be laid upon the hnen which is yet green, 

 and is to become red on being expofed to the fun ; after 

 fuch an expofure, the whole fllall be changed red or purple, 

 excepting only that fmall fpot which is covered by the 

 needle, which will ftill remain green. 



A plate of glafs, though it be three inches thick, vi'ill 

 not prevent the colour from changing purple by being laid 

 over it ; but the thinned; piece of metal will keep it wholly 

 green. The one being opaque, and the other pellucid, are 

 evidently the only x'eafons for this difference. 



If the coloured linen be fucceffively covered by three 

 pieces of paper, the one blacked with ink, the other in its 

 natural ftate, and the third rubbed over with oil, it will 

 change colour on being expofed to the fun in different de- 

 grees ; and that exaftly in proportion to the degree of trauf- 

 parence in each of the papers : moft of all in that which 

 was covered with the oiled- paper ; fomething lefs in that 

 covered by the paper in its natural ftate ; and leaft of all in 

 that which was covered v/ith the blacked paper, as that is 

 leaft tranfparent. 



The common Iieat of a fire, or that of a red-hot iron, 

 produces no change at all in the colour when green. ■ The 

 vapour of burning fulphur produces a little ; but the green, 

 which had not changed to purple by thefe experiments, im- 

 mediately clianged to it on being expofed to the rays of the 

 fun. 



PUR 



Thefe experiments were all made in the months of Ja- 

 nuary and February, by M. du Hamel, in Provence ; and 

 the fun having power to change the colour fo fpeedily tliere 

 in thefe cold months, probably in a warmer climate or fea- 

 foR the air would have been fufficient for the purpofe, with- 

 out the open fun ; fince it feems, from experiment, that 

 both the folar rays, and the light alone in a cloudy day, 

 can aft upon this colour. The light and heat of the fun 

 botlt aft on this colour : light is always fufficient to pro- 

 duce the effeft, biit the heat may eafily be too great or too 

 little ; and to do the whole in perfeftion, it muft be at a 

 certain m.iddle degree. 



This beautiful purple, if it can ever be brought into ufe 

 in dyeing, will have one very great advantage from its vif- 

 cofity. The pieces of cloth that had been itained by it 

 retained their colour, in fpite of feveral boilings in different 

 liquors, which M. du Hamel made them pafs through ; 

 and the colour, on examination, was found not to be fuper- 

 ficial, but penetrated the whole body of the ftuff, which 

 w^as tinged by it. There are many inconveniences which 

 muil naturally attend the ufe of this fubftance as a dye, 

 but they may, perhaps, all be got over by care and appli- 

 cation. It is very certain, that it is of too vifcid a nature 

 eafily to penetrate many fubftanccs ; but it is alfo certain, 

 that this might be obviated by did'olving it in fome proper 

 liquor. It appears very plainly, that the ancients had a 

 method of thus diflolving their purple ; but we neither 

 know what was their purple, nor what was its diflolvent ; 

 nor, which would be of much more confequence to us at 

 prefent, what is the proper diflolvent for ouf own. Mem. 

 Acad. Scien. Par. 1736. 



M. Reaumur has alfo difcovered another very different 

 kind of purple. This is produced in oval grains about a 

 quarter of an inch long, full of white liquor bordering on 

 yellow, which cover certain ftones or fands, about which the 

 buccina of Poiftou ufually aflemble. 



By the experiments M. Reaumur has made, it appears 

 that thefe grains are neither the eggs of the buccinum, nor 

 the feeds of any fea-plants, nor any rifing plants, but the 

 eggs of fome other unknown fifh. 



Thefe grains, being bruifed on a white linen, at firft only 

 tinge it yellow, and that infenlibly ; but in three or four mi- 

 nutes they give it a very beautiful purple red, provided the 

 linen be expofed to the open air ; for the air of a room, even 

 though the windows be open, will not do. This colour fades, 

 however, a little by repeated walhings. 



M. Reaumur concludes, from fome experiments he made, 

 that the effeft of the air on the liquor does not confift in its 

 taking away any particles of it, nor in giving it any new 

 ones, but only in its agitating it, and changing the ar- 

 rangement -of the parts that compofe it. He adds, that 

 the liquor of the buccinum, and that of the grains, feem 

 to be nearly of the lame nature ; except that the latter is 

 more watery, and only fahne ; vv'hereas the other is hot, and 

 pungent. 



P. Labat gives us the defcription of another purple dye, 

 produced by a tree growing in the Antilles. The juice of 

 this tree, when cut ftanding, is of a blood-red, and com- 

 municates the fame colour to cloths ; though, like the former, 

 it lofes much in often wafhing. 



Purple, Dyeing. See Dyeing. 



Purple Go/J. See Gold Precipitate, Sec. 



Purple, iji Medicine, an epithet applied to every difeafe, 

 in which eruptions of purple fpots, or petechia:, appear, and 

 thefe being ufually the accompaniments of fevers of every 

 kind in their worft and moll dangej-ous forms, fo purph 



1 2 fever 



