Ill 
Mr. Smithson on the colouring , & c . 
Its tinctures, or infusions, consequently, contain neither any 
alkali, nor any lime ; nor probably any acid, either loose or 
combined. This is unfavourable to the opinion of urine 
being employed in the preparation of turnsol. 
I put a little sulphuric acid into a tincture of turnsol, then 
added chalk, and heated ; and the blue colour was restored. 
It appears, therefore, that the natural colour of turnsol is not 
red, but blue, since it is such when neither disengaged acid 
or alkali is present. 
No addition of chalk brought the cold liquor back to a 
blue colour ; the carbonic acid absorbed by it, during the 
effervescence of the carbonate of lime, being sufficient to 
keep it red. 
Some turnsol was put into distilled vinegar. An efferves- 
cence arose ; and after some time the acid was become neu^ 
tralized. On examining the mixture with a glass, there were 
seen, at the bottom of the vessel, a multitude of grains like 
sand. It was found on trial that these grains were carbonate 
of lime ; probably of slightly calcined Carrara marble. 
When turnsol is treated with water till this no longer 
acquires any colour whatever, the remaining insoluble matter 
is nearly as blue as at first. 
Acids made this blue insoluble matter red, but did not 
extract any red tincture. 
Carbonate of soda did not affect it. 
If the vegetable part of this blue residuum is burned 
away, or it is washed off with water, a portion of smalt is 
obtained. 
On exhaling, on a water bath, a tincture of turnsol, the 
colouring matter is left in a dry state. 
