1818.] Edinburgh Transactions, Vol. VIII. Part II. 381 



of the other, and flies off in the state of water. Accordingly it 

 has been ascertained by experiment, that when muriatic acid 

 gas is made to pass through red hot lime, barytes, strontian, 

 &c. chloride of calcium, barium, strontium, &c. is formed, and a 

 considerable quantity of water is evolved. 



3. In Dr. lire's experiments it is obvious that the sal-ammo- 

 niac was partly decomposed ; for the liquid obtained was water of 

 ammonia ; therefore, the experiments are quite the same as if 

 muriatic acid gas had been passed slowly through a glass tube 

 heated to redness. 



4. But a glass tube contains several salifiable bases ; namely, 

 oxide of lead, oxide of manganese, soda, 8cc. These will be 

 partially converted into chlorides at a red heat, and of course 

 water will he formed. Sir H. Davy has ascertained by experi- 

 ment that this actually happens : he obtained water by passing 

 muriatic acid gas through red hot glass tubes. Here then we 

 see the source of the water in Dr. Ure's experiments, without 

 being under the necessity of considering it as previously existing 

 in sal-ammoniac. 



The same explanation will apply to the water which made its 

 appearance when Dr. lire substituted muriatic acid gas for sal- 

 ammoniac in his experiments. Into that part of the paper, 

 therefore, I need not enter. 



I may here notice an illustration which Dr. Ure employs in his 

 paper, and which is to be found likewise in Dr. Murray's paper, 

 which will be printed in a future number of the Annals; — it is that 

 sulphuric acid cannot exist without water. Now this is a mis- 

 take. I can procure sulphuric acid free from water, with great 

 ease, and I exhibited it last winter in that state to the Chemical 

 Class in the University of Glasgow. The mode of obtaining 

 anhydrous sulphuric acid, and the account of its properties in 

 that state, will be found in the Fifth Edition of my System of 

 Chemistry, vol. ii. p. 105. 



Dr. Ure's eudiometer for exploding combustible 

 gases is ingenious. It will be understood from the 

 figure in the margin. It consists of a glass tube, 

 sealed at one end and open at the other, bent into a 

 syphon shape, with the two legs of equal length. 

 The shut end is graduated, and furnished with me- 

 tallic wires in the usual way. The mixture of gas to \^J 

 be exploded is put into the graduated side ; a portion 

 of mercury is allowed to remain in the bend of the syphon, 

 filling it for example to a. Between a and the open moutli the 

 tube is tilled with common air. When the gas is to be exploded, 

 cover the open mouth of the syphon with the finger, and pass 

 an electric spark. The common air acts as a recoil spring, and 

 prevents the fracture of the tube. 



IV. On the- Laws which regulate the Distribution of the po- 

 larizing Force in Plates, Tubes, and Cylinders of Glass that have 

 received the polarizing Structure. By Dr. Brewster. — The 



