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fulphuric acid and a little potafh ; or in the ftate of ace- 
tite of alumina, in which it is combined with acetous 
acid. Acetite of alumina has only been introduced into 
dying fince the commencement of the eighteenth cen¬ 
tury. This mordant is now prepared, by pouring ace¬ 
tite of lead into a folutiori of alum : a double decompo- 
fition takes place, the fulphuric acid combines with the 
lead, and the compound precipitates in the form of an 
infoluble powder; while the alumina combines with the 
acetous acid, and remains dilTolved in the liquid. This 
.mordant is employed for cotton and linen, which have a 
weaker affinity than wool for alumina. It anfwers much 
better than alum, the cloth is more eafily faturated with 
alumina, and takes, in confequence, both a richer and a 
more permanent colour. Befides alumina, lime is fome- 
times ufed as a mordant. Clothriias a ftrong affinity for 
it; but in general it does not anfwer fo well, as it does 
not give fo good a colour. It is ufed either in the ftate 
of lime-water, or of fulphat of lime dilTolved in water. 
Almoft all the metallic oxyds have a ftrong affinity for 
doth ; yet only two of them are extenfively ufed as mor¬ 
dants, namely, the oxyds of tin and of iron. The oxyd 
of tin has enabled modern dyers greatly to furpafs the an¬ 
cients in the finenefs of their colours : by means of it 
alone, fcarlet, the brighteft of all colours, is produced. 
The method of producing the celebrated Tyrian purple 
dye is underftood at prefent, and the ffiell-fifh which 
yield the dye-ftuff are found abundantly on the coafts of 
Britain and France ; but no perfon thinks of putting the 
ancient mode in practice, becaufe colours equally beauti¬ 
ful can be produced at a fmaller price. This is owing 
to the employment of the oxyd of tin, which is ufed as 
a mordant in three ftates ; dilTolved in nitro-muriatic 
acid, in acetous acid, and in a mixture of fulphuric and 
muriatic acids. Nitro-muriat of tin is the common mor¬ 
dant employed by dyers. They prepare it by dilTolving 
tin in diluted nitric acid, to which a certain proportion 
of nmriat of foda, or of ammonia, is added. Part of the 
nitric acid decompofes thefe falts, combines with their 
bafe, and fets the muriatic acid at liberty. They pre¬ 
pared it at firft with nitric acid alone ; but that mode 
was very defective ; becaufe the nitric acid very readily 
converts tin to white.oxyd, and then is incapable of dif- 
folving it. The confequence of which was, the precipi¬ 
tation of the whole of the tin. To remedy this defeft, 
common fait, or fal ammoniac, was very foon added ; 
muriatic acid having the property of dilTolving white 
oxyd of tin very readily. A confiderable laving of ni¬ 
tric acid might be obtained, by employing as much ful- 
phurie acid as is juft fufficicnt to faturate the bafe of the 
common fait, or fal ammoniac, employed. When the 
nitro-muriat of tin is to be ufed as a mordant, it is dif- 
folved in a large quantity of water, and the cloth is dip¬ 
ped in the folution, and allowed to remain till fufticiently 
laturated. It is then taken out, and walked and dried. 
Tartar is ufually dilTolved in the water along with the 
nitro-muriat. The confequence of this is a double de- 
compofition ; the nitro-muriatic acid combines with the 
potafh of the tartar, while the tartarous acid dilfolves 
the oxyd of tin. When tartar is ufed, therefore, in any 
confiderable quantity, the mordant is not a nitro-muriat, 
but a tartrite of tin. 
Mr. Haulfman, to whom the art of dying lies under 
numerous obligations, has propofed to fubftitute acetit 
of tin for nitro-muriat as a mordant for cotton and linen. 
It may be prepared by mixing together acetit of lead and 
nitro-muriat of tin. This mordant is preferable for thefe 
Huffs; becaufe it is much more eafily decompofed than 
the nitro-muriat. Dr. Bancroft has propoled to fubfti¬ 
tute a folution of tin in a mixture of fulphuric and mu¬ 
riatic acid, inftead of nitro-muriat of tin, as a mordant 
for wool. This mordant, he informs us, is much cheaper, 
a’nd equally efficacious. It may be prepared by dilTolv- 
ing fo me what lefs than one part of tin in two parts cf 
N G. 
fulphuric and three of muriatic acid, at the degree of 
concentration at which they are commonly fold in this 
country. This mordant, like the others, muft be diffolv- 
ed in a ftifficient quantity of water, in .order to be ufed. 
Iron, like tin, is capable of two degrees of oxydation ; 
but the green oxyd abforbs oxygen fo readily from the 
atmofphere, that it is very foon converted into the red 
oxyd. It is only the red oxyd which is really ufed as a 
mordant in dying. The green oxyd is, indeed, fometimes 
applied to cloth ; but it very foon abforbs oxygen, and 
is converted into the red oxyd. This has a very ftrong 
affinity for all kinds of cloth. The permanency of the 
iron fpots or moulds on linen and cotton is a ftifficient 
proof of this. As a mordant, it is ufed in two ftates; 
in that of fulphat of iron, and acetit of iron. The firft 
is commonly ufed for wool. The fait is diffolved in wa¬ 
ter, and the cloth dipped in it. It may be ufed alfo for 
cotton ; but in mod cafes acetit of iron is preferred. It 
is prepared by diffolving iron, or its oxyd, in vinegar, 
four beer, &c. and the longer it is kept, the more is it 
preferred. The reafon is, that this mordant fucceeds 
beft when the iron is in the ftate of red oxyd. It would 
be better then to oxydate the iron, or convert it into ruft, 
before ufing it; which might eafily be done, by keeping 
it for fome time in a moift place, and fprinkling it occa- 
fionally with water. Of late, pyrolignous acid has been 
introduced inftead of acetous. It is obtained by diftilling 
wood or tar. 
That fpecies of mordant called the ajlringent principle , 
is derived from tan or nut-galls. It has a very ftrong 
affinity for cloth, and for feveral colouring matters : it 
is therefore very frequently employed. An infufion of 
nut galls, or of fumach, or any other fubftance containing 
tan, is made in water, and the cloth is dipped in this in¬ 
fufion, and allowed to. remain till it lias abforbed a 
fufficient quantity of tan. The French dyers call this 
operation cngallage. Silk is capable of abforbing a very 
great proportion of tan, and by that means acquires a 
very great increafe of weight. ManufadTurers fometimes 
employ this method of increafing the weight of (ilk. 
Tan is often employed alfo, along with other mordants, 
in order to produce a compound mordant. Oil is alfo 
ufed for the fame purpofe in the dying of cotton and 
linen. The mordants, with which tan moft frequently 
is combined, are alumina and oxyd of iron. Befides 
thefe mordants, there are feveral other fubftances fre¬ 
quently ufed as auxiliaries, either to facilitate the com¬ 
bination of the mordant with the cloth, or to alter the 
fiiade of colour. The chief of thele are, tartar, acetit 
of lead, common fait, fal ammoniac, fulphat, or acetit 
of copper, &c. 
Mordants not only render the dye permanent, but 
have alfo confiderable influence on the colour produced. 
The fame colouring matter produces very different dyes, 
according as the mordant is varied. Suppofe, for in- 
ftance, that the colouring matter be cochineal ; if we 
ufe the aluminous mordant, the cloth will acquire a 
crimfon colour ; but the oxyd of iron produces with it a 
black. Thefe changes, indeed, might naturally have 
been expected: for fince the colour of a dye fluff de¬ 
pends upon its affinity for light, every new combination 
into which it enters, having a tendency to alter thefe 
affinities, will naturally give it a new colour. Now, in 
all cafes, the colouring matter and mordant combine 
together : the colour of the cloth, then, muft be that 
which the particles of the dye and of the mordant, when 
thus combined together, exhibit. Indeed fome mor¬ 
dants may be confidered in the light of colouring matters 
alfo, as they always communicate a particular colour to 
cloth. Thus, iron communicates a brown colour, and 
iron and tan together conftitute a black. In dying, then, 
it is not only neceffary to procure a mordant, which has 
a fufficiently ftrong affinity for the colouring matter and 
the cloth, and a colouring matter which poffeffes the 
v illied o 
