120 Dr. Thomson's Experiments to determine the [Aug 



As yet I have not succeeded in procuring an iodide of carbon, 

 but I intend to pursue these experiments in a brighter season of 

 the year, and expect to obtain this compound. 



Article IV. 



Experiments to determine the Atomic Weight of various Metals 

 and Acids. By Thomas Thomson, Mb. FRS. 



I have in three preceding papers, one of which appeared in 

 vol. xvi. First Series ; and the other two in vol. i. of the present 

 Series of the Auiia/s of Philosophy given a set of experiments, 

 which appear to me to fix, with a degree of accuracy that cannot 

 easily be surpassed, the atomic weights of 20 different chemical 

 substances. I have also ascertained the weight of the combina- 

 tions with oxygen which these different substances form. These 

 compounds, including several bodies, whose atomic weight was 

 determined in my paper on the specific gravity of gases, make 

 the number of important chemical bodies, whose atomic weights 

 may now be considered as fixed with accuracy, amount to 65. 

 Indeed this number would be very materially increased if we 

 were to include the sulphurets and phosphurets and salts which 

 may be formed from these bodies — all of which may be deduced 

 witli perfect precision from the atomic weights laid down in these 

 papers.* 



* In the^Annales de Chimie et de Physique for July, 1820, torn. xiv. p. 321, 

 M. Gay-I.ussac has done me the honour to make some remarks upon the opinions 

 which 1 advanced in the Annals of Philosophy, xv SJK7, on the Composition of Phos- 

 phorous and Phosphoric Acids. It cannot be finally admitted, he says, that the oxygen 

 in these two acids is as 1 to 2, till I lay before the chemical world the experiments 

 proving that phosphuretted hydrogen gas contains exactly its own volume of hydrogen 

 gas, as MM. Thenard and Gay-Lussac in their Recherchcs Physico-Cbimiques, i. *I4, 

 have shown, that it contains about I § time its volume of hydrogen. I shall take this 

 opportunity of satisfying the doubts cf this very ingenious chemist. 



.In my paper on Phosphuretted Hydrogen Gas, printed in the Annuls of Philosophy, 

 viii. 87, and a translation of which was inserted in the Ann. de Chim. et dePhys. ii. 

 297, I have related a series of experiments which I made in order to determine this 

 point. I showed that the phosphorus might be removed by the cautious introduction of 

 oxygen gas in narrow tubes by electric sparks, and by heating it along with sulphur. In 

 all these trials, it was deprived of its phosphorus without any change cf bulk whatever. 

 Heating sulphur in this gas easily converts it into sulphuretted hydrogen gas without 

 any change of volume. These experiments cannot leave any doubt respecting the truth 

 of the fact, that phosphuretted hydrogen contains exactly its volume of hydrogen. 



The experiment related by Thenard and Gay-Lussac in their Recherchcs Physico. 

 Chimiques, i i.'1-l, consisted in heating potassium in phosphuretted hydrogen gas. The 

 phosphorus was separated, and K;0 volumes of the gas became 149 volumes. We have 

 not sufficient information given us by the authors to be able to explain it. When potas- 

 sium is heated in pure phosphuretted hydrogen, the volume cf the gas is not altered. 

 When it is heated in bihydroguret of phosphorus, or the hydrophosphoric gas of Davy, 

 the bulk of the gas is just doubled. It is probable that the gas used by these gentle- 



