WRITINGS OF JAMES SMITHSON. 59 



Turnsol. 



M. FOURCROY has advanced, somewhere, that turnsol is 

 essentially of a red colour; and that it is made blue by an 

 addition of carbonate of soda to it; and he says that he has 

 extracted this salt from the turnsol of the shops. 



If turnsol contained carbonate of soda, its. infusions should 

 precipitate earths and metals from acids. 



I did not find an infusion of turnsol in water to have the 

 least effect on solutions of muriate of lime, nitrate of lead, 

 muriate of platina, or oxalate of potash. 



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 effer- 

 vescence arose ; and after some time the acid was become 

 neutralized. 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 car- 

 bonate of lime; probably of slightly calcined Carrara 

 marble. 



When turnsol is treated with water till this no longer 

 acquires any color 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. 



