12 Sketch of the latest Improvements [Jan. 



removes any of the difficulties under which it labours, is, I own, 

 beyond my comprehension. But Berzelius has deserved so well of 

 chemistry, that he may be indulged in any innocent whim which 

 produces no deterioration. 



I sliould take up too much room were I here to give a table of the 

 weights of the atoms of bodies. I must satisfy myself with referring 

 to the different papers which I have inserted in the Ammls of Pht- 

 losophj on the subject, to the paper of Berzelius in the third 

 volume of the A^mals, in whicli will be found his table of the 

 weights of an atom of the simple substances, and to Dr. Wollas- 

 ton's scale of chemical equivalents. The weights given in these 

 three different tables do not always coincide with each other; but 

 in general a very near approach to coincidence will be perceived. 

 In some cases the weights that I have assigned are half those 

 given by Berzelius. The reason of this is obvious ; and the cir- 

 cunistaace can occasion no difficulty or ambiguity. 



II. Light and Heat. 



In the account of the progress of chemistry which I gave at the 

 beginning of last year, 1 had to state a considerable number of 

 important additions to the doctrine of heat, and its connection 

 with light ; but at present this department of the science is nearly 

 barren. M. Berard has repeated and confirmed the experiments of 

 Dr. Herschel on the heating power of the different rays of solar 

 light. He found the greatest heating power at the extremity of the 

 red ray. He likewise repeated the experiments of WoUaston, 

 *Ritter, and Bcickman, on the deoxidizing power of the solar rays. 

 He found it greatest, as they had done, in the violet ray ; and 

 traced it in a diminishing rate to the middle of the spectrum, 

 where it disappeared. 



Morichini, a Roman chemist, announced some time ago that, 

 when steel needles are exposed to the action of the violet ray, they 

 are converted into magnets. This experiment has been repeated ia 

 France, but has not been attended with success. 



III. Simple Supporters arid Comhustihles ivith their Compojinds. 



There are a considc-able number of facts to relate respecting this 

 branch of chemibtry. 



1. Iodine. — This singular substance was discovered some years 

 ago by M. Courtois, a saltpetre manufacturer in Paris. It was first 

 examined by Clement and Desormes, then by Sir H. Davy, and 

 lastly by Gay-Lussac. It is obtained from kelp by a very easy 

 process, whicli has been des;. lilicd in the Annals of Philosophy. 

 French kelp yields it in much greater abundance than British kelp. 

 Hence it would appear that the sea plants that yield it are more 

 abundant in the English Channel than on the east or west coast of 

 Britain. Iodine is in small crystals, which Dr. Wollaston has 

 ascertained to *be octahedrons. It has the metallic lustre, and 

 resembles plumbago in colour, though its lustre is considerably 

 i 



