244 REPORT— 1889. 



oxygen, and this latter combines witla the carbon, forming the combustible 

 oxide of carbon. Will not carbon partly deprive chalk gas of its oxygen ? 

 The experiment is made and it is found that it will. These results afford 

 an opportunity of calling attention to and explaining the changes which 

 go on in ordinary fires and in a furnace. 



Pkoblem XII. To determine the composition of salt gas, and the manner 

 in tuhich it acts on metals and oxides. — It has previously been demonstrated 

 that spirits of salt or muriatic acid is prepared by acting on salt with oil 

 of vitriol and passing the gas which is given off into water; the solution 

 has been found capable of dissolving various metals and oxides, chalk, 

 lime, &c., and as water alone does not dissolve these substances the effect 

 is apparently attributable to the dissolved gas, so it becomes of interest 

 to learn more of this gas in order that its action may be understood. It 

 is first prepared ; its extreme solubility in water is observed, and also the 

 fact that as it dissolves much heat is given out ; and it is noted that 

 although colourless and transparent it fumes in the air. How is its com- 

 position to be determined ? Is there any clue which can be followed up ? 

 Reference is made to the previous observations, and it is noted that its 

 solution dissolves various metals with evolution of hydrogen; water alone 

 has no such effect. Is this hydrogen derived from the water or from the 

 dissolved gas ? The gas alone is passed over heated iron turnings, and the 

 escaping gas is collected over water : it proves to be hydrogen, so evi- 

 dently salt gas is a compound of hydrogen with something else. How is 

 this something else to be separated from the hydrogen ? Do not previous 

 experiments suggest a method ? Yes, they have proved that hydrogen 

 has a mai'ked affinity to oxygen, and now it is recollected that on treating 

 muriatic acid with red lead — a substance rich in oxygen — a greenish- 

 yellow gas is obtained. The experiment is repeated on a larger scale and 

 the gas is examined. If it is contained together with hydrogen in salt 

 gas, perhaps salt gas will be obtained on applying a flame to a mixture 

 of the two gases just as water is from a mixture of oxygen and hydrogen : 

 the mixture is made and fired, and the result leaves little doubt that salt 

 gas does consist of hydrogen in combination with the greenish-yellow gas 

 — chlorine. Whence is this chlorine derived — from the salt or the 

 sulphuric acid ? 



The notes are again consulted, and it is seen that a solution of silver 

 in nitric acid gave a characteristic precipitate with muriatic acid but 

 not with sulphuric, so salt solution is added to the silver solution, and a 

 precisely similar precipitate is obtained, leaving little doubt that the 

 chlorine is derived from the salt. It is now easily realised that the iron 

 and zinc displace the hydrogen of the dissolved hydrogen chloride. 

 What happens when the oxides are acted on ? In addition to the metal 

 they contain oxygen, which is known to combine readily with hydrogen, 

 forming water; is water formed? Zinc oxide is therefore heated in 

 hydrogen chloride; a liquid is obtained which behaves exactly as a solu- 

 tion of hydrogen chloride in water. When the action is complete, and all 

 that is volatile has been driven off by heat, a solid remains very like fused 

 common salt — doubtless zinc chloride, since it is to be supposed that as the 

 hydrogen has taken the place of the zinc the chlorine has taken the place 

 of the oxygen. What, then, is the action of hydrogen chloride on chalk ? 

 It evidently not only separates the chalk gas from the lime, but also 

 dissolves this latter. What is formed ? Dry (unslaked) lime is therefore 

 heated in a current of hydrogen chloride. It behaves just as zinc oxide, 



