26 On the Use of Tincture and Braxil Wood, &c. [Juuy, 
Tartaric acid also gives a very fine yellow colour, but it soon 
fades and becomes dull, in proportion to the weakness of the 
acid. If, for instance, it is diluted with five parts of water, it 
gives a less lively colour than citric acid mixed with 15 or 20 
parts of water. 
Malic acid acts nearly like tartaric acid. 
Concentrated oxalic acid produces an orange colour which 
becomes gradually yellow. Diluted with one part of water, it 
gives a yellow colour, which remains pretty good. If the acid 
is diluted with three parts and more of water, the yellow colour 
at first produced disappears in a few minutes. 
Succinic acid gives a yellowish colour which soon fades, and 
benzoic acid has scarcely any action. 
It occurred to me that the fine yellow colour which succeeds 
the red colour of Brazil wood, when it is subjected to the action 
of phosphoric or citric acid, might be employed in the art of 
dyemg. To ascertain this, I tried at several times to dye wool 
by means of the above-mentioned substances, and these trials 
afforded results which exceeded my expectation. Some woollen 
manufacture dipped into a boiling bath of Brazil wood, acquired 
a yellowish-red colour, but it was dull. If, after washing and 
draining, it is dipped for a few minutes in a boiling and very 
dilute solution of phosphoric acid, or lemon juice, diluted with 
water, a very bright yellow colour is immediately produced. 
As phosphoric acid is too dear a substance to be employed 
with advantage in dyeing, I tried as a substitute acidulous 
phosphate of lime obtained by treating bones with sulphuric acid, 
and I found that this substance acted precisely in the same 
manner, and gave as fine a colour as that produced by pure 
phosphoric acid. Woollen manufacture dyed yellow, by means 
either of an acidulous phosphate or lemon juice, may be sub- 
jected to the strongest soaping, without the colour undergoing 
any alteration. 
[have had no opportunity of ascertaining by direct experi- 
ment whether this colour is permanent, and resists the action of 
the sun; it may be admitted that even if the colour produced by 
the action of lemon juice is not permanent, that given by the 
acidulous phosphate, on the contrary, will be so, as being a 
combination of the colouring principle with a substance which 
is perfectly unalterable by water, air, or heat. 
Silk is also susceptible of receiving a fine yellow colour by the 
process which has been described; but as to cotton and linen, 
the very incomplete experiments which I have had an opportu- 
nity of performing, have not afforded a satisfactory result ; it 
might, perhaps, be possible to succeed if the substance to be 
dyed was previously animalized. It is, however, worthy of 
remark, that paper, as I have already observed, receives and 
retains this colour with all its brightness. 
