194 Green Ore of Uranium. 



potatoe dissolves in the boiling water, forming a somevvliat 

 viscid liquid, which envelopes every particle of the precipi- 

 tated calcareous salt (usually Selenite, sometimes Carbonate 

 of Lime) renders them shppery, so to speak, and prevents 

 their mutual contact and cohesion. After a month's ser- 

 vice, the boiler is emptied, and new potatoes added along 

 with the charge of water. 



22. Flowers of the common Mallow (Malta Sylvestris) 

 an excellent Testof Alkali. — M. M. A. Payen and A. Cheva- 

 ]ierstate,thatan alcoholic infusion of these flowers (previously 

 dried by a steam heat out of contact of light) gives a sen- 

 sible tinge of green on being mixed with water containing 

 5g^-g55 part of potash, xoVo P^''^ "^ Carbonate of Soda and 

 ■^\ of lime water. 



According to the same chemists, the colouring matter of 

 the fruit of the Cerasus Mahaleb (wood of St. Lucie,) is an 

 excellent test of acids, but inferior in delicacy to litmus. 

 Infusions are more sensible to change of colour than colour- 

 ed paper. 



23. Method of colouring Alum Crystals. — In makingthese 

 crystals, the colouring should be added to the solution of 

 alum in proportion to the shade which it is desired to produce. 



Coke, with a piece of lead attached to it, in order to make 

 it sink in the solution, is the best substance for a nucleus ; 

 or if a smooth surface be used, it will be necessary to wind 

 it round with cotton or worsted ; otherwise no crystals wil] 

 adhere to it. 



Yellow. — Muriate of iron. - 



JBZwe.— Solution of Indigo in sulphuric acid. * 



Pale Blue. — Equal parts of alum and blue vitriol. 



Crimson. — Infusion of Madder and Cochineal. 



Black. — Japan ink, thickened with Gum. 



Green. — Equal parts of alum and blue vitriol with a few 

 drops of muriate of iron. 



Milk white. — A crystal of alum held over a glass contain- 

 ing ammonia, the vapour of which precipitates the alumina 

 on its surface. 



24. Green Ore of Uranium. — R. Phillips has ascertained 

 that the green ore of Uranium from Cornwall, contains 



