Royal Society. 355 



The co-efficient of the equation depending on the moon's distance 

 from the sun, affords the means of calculating the sun's horizontal 

 parallax. For this purpose Laplace has computed this co-efficient 

 with greater accuracy than the rest ; and he makes the sun's parallax 

 nearly 9". The author's theory gives it little more than 8", which 

 is very near the mean of the various results obtained by the obser- 

 vation of transits. He thinks that there is, therefore, great reason 

 to conclude that its true value is about this quantity. 



Feb. 10. The reading of a Paper, entitled, " On a New Com- 

 bination of Chlorine and Nitrous Gas." By Edmund Davy, Esq. 

 F.R.S. M.R.I. A. Professor of Chemistry to the Royal Dublin So- 

 ciety. Communicated in a Letter to Davies Gilbert, Esq. late Presi- 

 dent of the Royal Society ; was commenced. 



Feb. 1 7. The reading of Professor Davy's Paper was resumed 

 and concluded. 



In the course of his experiments on a new test for chlorine gas, an 

 account of which was lately read to the Royal Society, the author 

 was induced to examine the gases produced by the mutual action of 

 nitric acid and different chlorides, and also of the nitric and muriatic 

 acids on each other. When fused chloride of sodium, potassium or 

 calcium, in powder, is treated with as much strong nitric acid as is 

 sufficient to wet it, a considerable action takes place : cold is produced, 

 and a gas of a bright reddish or yellowish colour is copiously evolved, 

 which evolution is promoted by applying a gentle heat. This gas, 

 especially in the early stage of the process, appears to be a mixture 

 of chlorine and another gas, distinguished from it by the great fa- 

 cility with which it is absorbed by water. From this circumstance, 

 and from its also exerting a considerable action upon mercury, its 

 properties cannot be satisfactorily ascertained by collecting it in con- 

 tact with either of these fluids ; but as it is much heavier than com- 

 mon air, the author was enabled to collect it in sufficient quantity 

 for examination, and nearly in a pure state, from a tubulated retort 

 by means of a bent tube reaching to the bottom of small narrow- 

 mouthed bottles, with ground stoppers. 



The gas, when thus obtained, is of a pale reddish yellow colour ; 

 has an odour somewhat resembling that of chlorine, though less pun- 

 gent. From its strong affinity for moisture, it fumes when brought 

 into contact with the air. In its ordinary state of dryness it destroys 

 vegetable colours, readily bleaching turmeric paper : litmus paper, 

 however, is reddened by it before it is bleached. But when carefully 

 dried by means of fused chloride of sodium, it does not affect those 

 substances. This gas does not support combustion ; but the biful- 

 minate of silver explodes in it. 



The author next describes its action upon phosphorus, sulphur, 

 antimony, arsenic, bismuth, tin, copper, zinc, iron, lead, gold, silver, 

 platina, mercury, sulphuric ether, alcohol, oil of turpentine, naphtha, 

 concentrated muriatic acid, iodine, and bromine. With hydrogen 

 gas it forms a mixture which explodes when ignited. 



The general conclusion which the author draws from his experi- 

 ments, is that this gas is an actual compound of chlorine and nitrous 



2 Z 2 eras, 



