Tin. 
411 
1st. Of the tin. The common tin frequently con- 
tains lead ; and sometimes copper ; with this admixture, 
no fine scarlet can be procured. Both lead and copper 
alter the crimson and the scarlet tinge ; the latter metal 
saddens the colour. But, out of eighty grains of common 
tin from an ingpt such as are usually sold in Philadelphia, 
I procured neither lead or copper. I dissolved it in nitric 
acid, which calcined all the tin : the oxyd being washed, 
shewed no trace of lead with sulphuric acid. 
No tin is so fit for the purpose as that called the grain 
tin, and even that is not always free from contamination. 
Sly. Of the acid. A scarlet dyer ought to make his own 
aqua fortis in glass. In the common way of manufacturing 
this acid, if iron stills or retorts are not used, iron heads 
to the stills, are. Hence, it is scarcely possible that 
the acid should not be contaminated with iron. This 
can be ascertained by tincture of galls, or prussiat of pot- 
ash ; and though the triple nature of this last salt is liable 
to objection, it will sufficiently answer the purpose. 
Nitric acid is also contaminated by an admixture of 
muriatic ; owing to the common salt contained in com- 
mon salt petre ; and also of sulphuric acid, owing to the 
impurity of the oil of vitriol usually employed, which 
comes over in the form of sulphurous acid gas. But I 
do not know that these are very objectionable in the pro- 
cess. The addition of nitre tends to saturate the superflu- 
ous sulphuric acid. 
3ly. Of the sal-ammoniac. This salt is made accord- 
ing to modern processes, from alkali procured by the dis- 
tillation of animal substances in long cylindrical iron re- 
torts. It ought to be previously examined for iron, which 
uniformly gives a violet tinge to the cochineal colour. 
4ly. Of the nitre. I do not think it worth while to 
purify this salt. The common impurities, except iron, 
do no damage. 
Vo l. III. 3 E 
