M. Simon oti Jervine^ a neiio Vegetahle Base. 29 



together withdrawn, these beautiful tints all vanish in a mo- 

 ment. We have then in this easy experiment a palpable 

 proof that it is the distance between the surfaces only which 

 determines the colours of thin plates. 



The plate of mica which we employ should be about the 

 size of a page in an octavo book*, and about the thickness of 

 a card. This size is convenient to hold with both hands, and 

 the circumference of such a plate of mica will admit of several 

 distinct plates of air. Films should be made between differ- 

 ent laminae of the mineral, by which means we shall possess 

 films of air, covered with plates of mica of different degrees 

 of thickness. 



The colours may be seen very well with the naked eye, but 

 they appear more beautiful when examined with a mag- 

 nifier. The plate of mica should be held near a window, so 

 as to reflect the light. 



Looking over your Number for October, p. 375, I saw Dr. 

 Readers paper " on a permanent soap-bubble." I soon made 

 this beautiful experiment, and beheld the splendid colours as 

 described. 



In Dr. Readers permanent soap-bubble we have a liquid 

 film, and in my experiment a film of air. 



I am, Gentlemen, yours, &c., 



London, Nov. 1, 1837. James Walgon. 



VIII. Jerviney a new Vegetable Base, By Edward Simon 

 of Berlinf, 



I HAVE been so fortunate as to discover in the roots of the 

 Veratrum album (Radices Hellebori albi), along with ve- 

 ratria, a new vegetable base possessing some very remarkable 

 properties. 



The alkaline extract from the root is boiled several times 

 with water, which has been acidulated with muriatic acid, 

 and the clarified acid liquid precipitated by a solution of pure 

 carbonate of soda. It is necessary that the carbonate of soda 

 be free from any mixture of sulphate of soda. The precipi- 

 tate is dissolved in alcohol : the solution is then decolorated by 

 means of carbon, and is separated almost, but not completely, 

 from the alcohol by distillation. The residuum consolidates 

 on cooling into a crystalline mass. This is then subjected to 

 pressure, by which it is freed from the greatest part of the 

 uncrystallizable veratria. If the pressed cake be once more 

 moistened with alcohol and pressed, we obtain the new base 

 tolerably pure. 



* Such plates of mica may be had of Knights, Fos^tcr Lane. 

 "t From PoggcndoifTs Annalen, vol. xlix. p. 569. 



