C H £ M I 
of this kind ate already ufed in feveral manufactures. 
The very finall quantity of tin required to cover the fiir- 
face of copper, is fufprifing ; Bayen and Charlard having 
determined, that a veffel of nine inches in diameter, and 
three inches three lines in depth, did not gain more than 
twenty-one grains by tinning. This (mall quantity is, 
neverthelefs, fufficient to prevent the dangers which might 
arife from the ufe of copper veftels, provided care Ire taken 
that fubftances capable of diffolving the tin be not fuf- 
fered to remain too long a time in the veftels ; and more 
efpecially that the tin be frequently renewed : as the fric¬ 
tion, heat, and action of fpoons, with which the included 
fubftances are ftirred, deftroy it very quickly. There is 
likewife another caul'e of apprehenfion relpefting the tin 
ui'ed by braziers in tinning, &c. It is often alloyed with 
one-fourth of its weight of lead ; and in this cafe the bad 
effedts of the latter metal are much to be feared, as it is 
knowm to be very foluble in acids and fat fubftances. 
La Folie, of Rouen, well known by his chemical labours 
refpefling the arts, and the ufeful difeoveries with which 
lie has enriched the art of dying, of pottery, and a great 
number of manufadtures, propofes, in order to avoid the 
inconvenience and danger of tinning copper, thatfauce- 
pans of forged iron covered with zink might be ufed, 
which, as we have hlready feen, is not productive of any- 
dangerous effects. Many perfons have already ufed thele 
veffels, and have been fenlible of their advantages. It is 
much to be defired that the ufe of thefe veftels may be¬ 
come more general. 
Copper and lead unite very eafily by fufion, as the for¬ 
mation of the leaves of eliquation prove. But this com- 
pofitionis not permanent; for the lead melts with a gentle 
beat, and abandons the copper. The refpedtive affinities 
of lead and copper for acids have not yet been accurately 
determined. 
Copper and iron are capable of uniting either by fufion, 
or in the way of foldering; yet this combination does 
not eafily fucceed. When a mixture of the two metals 
is melted in a crucible, the iron is found in pieces in the 
copper, without being perfectly united. Copper decom- 
pofes, according to Monnet, the mother water of fulphat 
of iron, though iron has a ftronger affinity with acids 
than copper. 
The fulphuric acid does not ad on copper but when 
concentrated and boiling; much fulphureous acid gas is 
difengaged during the folution. A brown matter, of 
the confidence of a thick fluid, containing oxyd of cop¬ 
per, and a portion of the oxyd combined with the ful¬ 
phuric acid, are fbund at the bottom; from which, by 
the addition of water and filtration, a blue folution is 
obtained: if this be evaporated to a certain point, and 
fuffered to cool, rhomboidal long cryftals are afforded, of 
a beautiful blue colour, called fulphat of copper, or blue 
vitriol. If the folution, inftead of being evaporated, 
be left expoled a long time to the air, it affords cryftals ; 
but a green oxyd is precipitated. All the oxyds of cop¬ 
per when formed or dried in the air, are of this colour. 
Sulphat of copper has a very ftrong ftyptic tafte, ap¬ 
proaching even to caullicity; it is a ftrong poifon. When 
expoled to heat, it very loon melts, loles its water of 
cryftallization, and becomes of a bluifli wffiite; a ftrong 
heat is required to feparate the fulphuric acid, which ad° 
heres much more ftrongly to the oxyd of copper than to 
that of iron, though the iron indeed decompoles the di¬ 
lutions of copper by a different attra&ion, that of the 
iron for oxygen. Sulphat of copper is decompofed by 
magnefia and by lime ; the precipitate formed by either 
of thefe fubftances is of a bluilh white, but befcomes 
green if dried by expolure to the air. A fimilar precipi¬ 
tate is obtained with alkalis. If the precipitate obtained 
by potalh be heated with cauftic potalh, the precipitate 
loles its colour, and becomes brown : in this operation, 
the copper lofes a portion of its oxygen, for the brown 
-precipitate contains lefs oxygen than the blue; but it is 
not known whether this laft oxygen combines with the 
i 
S T R Y. 307- 
alkali. The proportions of the conftituer.t principles of 
fulphat of copper, are known by decompofing it with al¬ 
kalis. Soda and ammoniac produce the fame effedl ;rs 
potalh; but, if the latter be in excels, the ammoniac 
has the property of re-dillblving the precipitate, and giv¬ 
ing it a blue colour. The hydro-fulphures decompofe 
this fait, and the Pruffiats alfo. Several metals have the 
fame property : if a plate of iron, zink, or tin, be plunged 
into a folution of this fait, the copper will be precipitated. 
Scheele's green is produced by the decompqlition of ful¬ 
phat of copper with arfenit of potalh. Melt potaffi in 
water by the affiftance of heat; add white oxyd of arfe- 
nic, or arfenious acid, to the point of faturation. Or, 
Take a hot folution of fulphat of copper, pour it into 
arfenit of potaffi; pour it by little and little, and ftir it 
with a glafs tube. Then let it fettle, and a precipitate 
is thrown down; decant the liquor, and on the refidue 
pour a little hot water, and ftir it well; then pour off 
the liquor afrelli; walh twice with warm water in the 
fame manner; put the whole to filter, and then let it 
dry; a beautiful green colour is produced, not aftefted 
by air, and therefore very convenient for painters. Ar¬ 
fenit of copper is formed in this experiment. But if, in¬ 
ftead of arfenit of potalh, the arfeniat be ufed, the pre¬ 
cipitate is ftill of a very beautiful colour, and arfeniat of 
copper is formed. 
The nitric acid diffolves copper with great rapidity in 
the cold; a large quantity of very red nitrous gas'being 
at the fame time difengaged. This is the method ufed by 
Dr. Prieltley to obtain a very ftrong nitrous gas. A por¬ 
tion of the metal reduced to the ftate of oxyd is preci¬ 
pitated in the form of a brown powder, and is feparated 
by the filter. The filtrated folution is of a much deeper 
blue than the fulphuric iolution, which (hows that the 
copper is more perfectly oxydated; by previous and care¬ 
ful evaporation, cryftals may be obtained in cooling, 
refembling bundles of divergent needles. Nitrat of 
copper is of a very bright blue, and is fo cauftic, that 
it may be employed in corroding the excrefcences which 
arife on the (kin; it melts, according to Sage, at 
the temperature of twenty degrees of the thermometer 
of Reaumur, and detonates on burning coals, though 
this phenomenon is fcarcely lenfible, on account of the 
large quantity of water it contains. When melted in a 
crucible, it emits large quantities of nitrous vapour, 
which may be collected by diftillation ; when dried, its 
colour is green ; an increafe of the heat converts it to a 
brown,'in which ftate it is a pure oxyd of copper. Four- 
croy diltilled this fait with the pneumatic apparatus, and 
obtained much nitrous gas, a finall quantity of carbonic 
acid, and a frnall quantity of vital air ; it was converted 
into a brown oxyd by this operation. Ni'.rat of copper 
attracts the moilture of the air, but it may be prelerved 
a long time in dole veftels ; in a dry and hot air it be¬ 
comes covered with a green effioi eicence. It is very 
foluble in water, and rather more fo in hot than in cold 
water. The folution expoled to the air in (hallow veftels, 
or quickly evajforated in hot and dry weather, leaves an 
oxyd of the fame green colour as the cryftals of the fait 
have in fimilar circumstances. But, not to lofe the nitrat 
of copper which is obtained in coining, by precipitating 
the lilver of the nitrat by means of copper, there is form¬ 
ed of it in England, what id called blue earth, or blue 
ajhes , ufed for painting or ltaining paper. To a folution 
of copper in nitric acid, they add powdered chalk; ftir 
the mixture to facilitate the decompolition of the nitrat 
of copper; there ffiould be a finall excels of the nitrat 
of copper, that all the lime may be abforbed ; and, that 
the precipitate, which takes place the moment the mix¬ 
ture is made, may be ajprecipitate of copper only, let 
this precipitate fettle ; then pour off the liquor, which is 
nitrat of lime, and walh feveral times; then put the whole 
into a cloth, that it may drain at leifure. ^Vith this pre¬ 
cipitate, which is of a faint green colour, commonly 
called mountain sreen, blue alhes are prepared: for which 
purpofej, 
