Chemistry and Physics. 601 



clay-lined retort is filled seven-eighths full of coke, ignited and 

 raised to a white heat by an air blast. The retort is then closed 

 and a cheap hydrocarbon like crude petroleum or coal tar is in- 

 jected into it for about twenty minutes, or until the temperature 

 has fallen below the proper "cracking" point, the gas thus 

 generated passing through a sprinkling tower and a filter into a 

 gasometer. The air blast is again turned on and the process is 

 repeated indefinitely with periodical renewal of the coke and 

 removal of the ashes. The product contains about 96 per cent of 

 hydrogen, and by passing it through suitable absorbents it can 

 be further purified to about 98*4 per cent. The total cost is 3 or 

 4 cents per cubic meter. The method of passing superheated 

 steam over red-hot iron is little used now, as is also the method 

 of conducting water-gas through suitable absorbents so that the 

 hydrocarbons and the carbon monoxide are removed. However, 

 another process employing water gas is increasing in application. 

 In this the water gas, consisting mainly of carbon monoxide and 

 hydrogen, is compressed and cooled to the liquefying point of 

 carbon monoxide. Upon relieving the pressure the expansion 

 cools the mixture still further, so that most of the impurities 

 separate in the liquid form, while hydrogen 97 or 98 percent pure 

 passes off. The mixture consisting largely of liquefied carbon 

 monoxide is afterwards vaporized and used in gas engines for 

 power. 



At European army posts hydrogen for military balloons is com- 

 monly made from scrap iron and sulphuric acid. For field opera- 

 tions zinc is used in place of iron with sulphuric acid, but there are 

 three other more modern means of generating hydrogen for field 

 purposes, called the " Hydrolith," " Silicol," and "Hydrogenite " 

 processes. Hydrolith is calcium hydride, which reacts directly 

 with water as follows : CaH, + 2H 2 = Ca(OH) 2 + 2H 2 . It is a 

 convenient but expensive method. The silicol process consists in 

 treating powdered ferro-silicon or mangano-silicon with water 

 and caustic soda. It does not appear to have gained extensive 

 use on account of the troublesome manipulations and the difficulty 

 of controlling the evolution of gas. Hydrogenite is composed of 

 ferro-silicon (containing 90 to 95 per cent of metallic silicon) 25 

 parts, caustic soda 60 parts and dry slaked lime 20 parts. This 

 mixture of finely powdered dry materials, compressed in blocks, 

 decomposes when a hot wire is thrust into it, according to the 

 equation, Si + Ca(OH), + 2NaOH = Na 2 Si0 3 + CaO + 2H 2 .- 

 Chem. Migr., xx, No. 6. h. l. w. 



2. The Density of Lead from Ceylon Thorite. — Having pre- 

 viously found, as the result of an examination of less than 1 g. of 

 lead from Ceylon thorite, that this lead gave an. atomic weight 

 rather more than a unit higher than ordinary lead ; Frederick 

 Soddy has extracted about 80 g. of this metal from 20 kg. of the 

 finest grade of the same thorite. This product and a similar 

 weight of ordinary test lead were carefully purified by identical 

 processes and finally melted in a vacuum and carefully cast in 



