459 



NATURAL-PHILOSOPHICAL COLLECTIONS. 



Estimation of the Vegeto-Alkali in Peruvian Bark. — It is often important in 

 pharmacy to be able to tell the value of a sample of bark, by ascertaining the 

 quantity of quinia or cinchonia which it contains. MM. Henry and Plisson, 

 and also M. Tilley, have published processes for this purpose. Professor Gobel 

 Applies the following method to obtain the same end : — Two ounces of powdered 

 bark are acted upon, at successive times, by sixteen ounces of water and 1 80 

 grains of muriatic acid, specific gravity 1.13, ebullition being occasioned ; all the 

 liquids are to be put together, and caustic potassa added, which produces a brown 

 precipitate ; this is to be re-dissolved in dilute muriatic acid, again precipitated, 

 ^d so on, until the precipitate is quite white; it is then to be dried, and treated 

 with cold strong alcohol, to separate the quinia and cinchonia from each other. 



"M. Veltman has devised the following process, which may be applied to small 



quantities ; it is easy of execution and exact : 55 grains of the bark in fine powder 



is to be mixed with an equal quantity of washed siliceous sand, the grains of 

 which are about half the size of poppy seed ; this is to be well mixed with five 

 drops of muriatic acid, and 20 drops of alcohol, and pressed lightly into a glass 

 tube 4| inches long, and 0.6 of an inch in diameter, one end of which has been 

 covered with a little piece of muslin, and then inserted into a close vesseL The 

 other end of this tube is to be connected by a bent tube with a small flask filled 

 with a mixture of an ounce and a half of alcohol, and 20 drops of muriatic acid ; 

 the bent tube should be 0.2 of an inch in diameter ; one end should go to the 

 i)Ottom of the flask, the other should reach the surface of the mixed bark and 

 sand. The alcohol in the flask is then to be boiled by a small spirit lamp. It 

 will pass through the tube and extract all that is soluble. If the ebullition is 

 performed slowly, the last drops of alcohol pass nearly colourless. The reddish 

 ^)rown alcoholic tincture is to be precipitated by hydrated lime ; after twelve hours 

 it is to be separated by a filter, the liquor is to be rendered slightly acid, evapo- 

 irated until in a soft state; then dissolved in 120 grains of water, and precipitated 

 by a few drops of caustic ammonia. The precipitate being dried, indicates the 

 quantity of alkali in tlie bark. In this way, M. Veltman found that from 3.3 to 

 6.0 parts of vegeto-alkali were combined in 100 parts of diiFerent varieties of bark. 

 IPuU. Univ. C. XX. 297. 



' Svanberg^s Researohes on the Heat of the Planetary Space. — It is known that 

 Fourier, in his valuable researches into this subject, deduced from the laws of radiant 

 heat that the temperature of the planetary space is — 50° Cent. =58 Fahr., and that 

 the earth has nearly reached its limit of cooling. Svanberg has built his researches 

 ppon a different principle, and has obtained the same result. From his letter to 

 jBerzelius on tlie subject, we extract the following : — " Led by these considerations, 

 Snd by the many known affinities between light and heat, which are especially 

 remarkable in the acknowledged property of solar light to develope heat in opaque 

 (ind imperfectly tranparent bodies, I began by supposing that the planetary space 

 (considered as perfectly pellucid) never undergoes any change of temperature 

 either from the action of light or of radiant caloric, and that, therefore, the ca- 

 •pacity for elevation of temperature above what reigns in the etherial regions, can 

 exist only within the limits of the planetary atmosphere. Further, that the ra- 

 pidity of the change of temperature at an indefinite height above the surface of 

 the earth, is always proportional to the rapidity of the atmosphere's corresponding 

 change of capacity to absorb light. In this way I obtained the temperature of 

 the atmosphere, (expressed in a function of an indefinite height above the earth's 

 surface) containing only two arbitrary constants, of which the one is also a func- 

 tion of the time, and is determined always by immediate observation of the given 



