Chemical Science. J 79 



sufficient, and it is desirable that he should make the characteristic 

 principle of this root better known. — Ann. tie Clam. xxvi. 219. 



14. Oil of the Dahlia. — At the same that M. Payen had oc- 

 casion to signalize the existence of a peculiar vegetable principle in 

 the Dahlia*, he noticed, in connexion with it, a peculiar vegetable 

 oil. Further experiments with the oil have shown it to contain two 

 distinctsubstances,the one acrystallinebody havingmanyof the cha- 

 racters of benzoic acid, and the other a fluid uncrystaliizable at low 

 temperatures. Both are soluble in alcohol and acetic acid, but almost 

 insoluble in water; they may be separated by cooling the mixture t6 

 the crystallizing point, decantation, and pressure of the crystals.— 

 Juur. de Phar. x. 239. 



15. Crystallization of Bitumen. — The notes of proceedings of the 

 Royal Academy of Medicine, at Paris, mention indications of the 

 crystallization of bitumen in compressed polyhedrons, announced 

 by M. Sido; and this gave occasion to the remark by some mem- 

 bers, of the appearance of small granular opaque crystals in 

 rectified petroleum, when preserved for a length of time. — Jour, 

 de Phar. x. 307. 



16. Effect of light on colour of Sodalite. — Mr. Allan observed a 

 very interesting phenomenon, in relation to the action of light upon 

 the colour of theSodalite of Greenland. When the massive variety is 

 broken up, many portions of it have the most brilliant pink colour; 

 but after a day's exposure to the action of light this colour 

 almost entirely vanishes. Having broken a specimen into 

 two, Mr. Allan kept one of them in the dark, and exposed the other 

 to light; the specimen kept in the dark retained its pink colour 

 unimpaired, while the other lost it almost entirely. — Edin. Juur. 

 Sci. X. 181. 



17. Cleansing of Gold Trinkets. — Dr. Mac CuUoch proposes to 

 cleanse gold trinkets, such as chains, 4"c., by boiling them in ammonia 

 instead of acid. Such trinkets are generally made of an alloy con- 

 taining much copper, and therefore require what the jewellers call 

 colouring, that is the removal of copper, so as to leave a surface of 

 pure gold. After some time the surface wears oft' and the trinket 

 requires cleaning, or a repetition of the former process : this is 

 generally done by an acid, but as gold is dissolved in that way and 

 consequently (ine work, after two or three cleanings, very much 

 injured, Dr. Mac Cnlloch recommends the use of ammonia, which 

 docs not involve this injury, and which can be applied by any per- 

 son as well as the jeweller. The effect depends upon the power 



* Quarterly Journal, xvi. p. 87. 

 N2 



