^•232 Scienlijie Intelligence. [March, 



V. An Account of the Slate of the Barometer, Thermometer^ and 

 Wind, during the late Hurricane, at the Island of St. Thomas's, 

 in the West Indies, as observed on Board H.M.S. Salisbury. 

 Communicated by Col. Beaufoy, F.R.S. 



V. Method of determining the Specif c Gravifi/ of Gases. 



In the first volume of the Memoirs of the Wernerian Natural 

 History Society of Edinburgh, the members of that Society did 

 me the honour to insert a paper of mine on oletiant and carbu- 

 retted hydrogen gases. In that paper I have given an account 

 of the method which I have long been in the habit of following 

 for taking the specific gravity of gases. I have reason to believe 

 that this method has been generally followed in Great Britain 

 ever since I made it knov.-n. But if we are to judge from the 

 account which Biot gives of the mode of taking the specific 

 gravity of gases in his Traite de Physique, and from the descrip- 

 tion which Berzelius gives of his own experiments to determine 

 the specific gravity of sulphurous acid gas,* it does not appear 

 to me that the chemists on the continent are aware of the faci- 

 lity with which the specific gravity of gases may be taken. 



My method is foundedon a well-known fact that when two gases 

 are mixed their bulk does not alter, I have a large glass flask fitted 

 with a stop-cock, I weigh this flask as accurately as possible ; 

 then exhaust it, and weigh it again. The loss of weight sus- 

 tained is equal to the quantity of common air drawn out, and is 

 less or more according to the size of the flask and the goodness 

 of the exhaustion. Let it be = a. I then fill the flask with the 

 .gas whose specific gravity I want, taking care to exhaust the 



• See the last number of the Annals of Philosophy, 



