CHEMISTEY. 



87 



from 80 tons of water of 72, in order to change 

 it into ice. But in practice we find here ex- 

 actly the same state of things as in the opera- 

 tion of the steam-engine. Theoretically a steam- 

 engine ought to produce at least TOO units of 

 force (foot-pounds) for every unit of heat con- 

 sumed ; in practice, good machinery only pro- 

 duces from about 70 to 100 foot-pounds from 

 about one-tenth to one-seventh part of the 

 theoretical amount. In the best ice-machines 

 thus far constructed, instead of freezing 80 

 tons of water, for every ton of coal consumed, 

 only from about 8 to 11 tons of ice are pro- 

 duced, also, from one-tenth to one-seventh 

 part of the theoretical amount ; proving, thus, 

 the remarkable fact that, in both the steam- 

 engine and the ice-machine, exactly the same 

 relation exists between the theoretically cal- 

 culated effects and the practical results. 



As, however, all the best ice-machines ac- 

 complish the conversion of the heat of the fuel 

 into the freezing operation by the intervention 

 of a steam-engine, the fact that they practi- 

 cally produce only from one-tenth to one-sev- 

 enth of the amount of the cold they theoreti- 

 cally should produce, is solely due to the other 

 fact, that the steam-engine itself practically 

 produces only from one-tenth to one-seventh 

 of the amount of power which would be 

 strictly equivalent to the number of heat-units 

 consumed. It must not be lost sight of that it 

 is only the power of the steam-engine which 

 generates the cold in the freezing-machines, 

 and that, therefore, improvements in the steam- 

 engine, which bring its practical results nearer 

 to the theoretical standard, will at once exert 

 their influence on the amount of ice the ice- 

 machines can produce, and, consequently, also 

 on the cost of the ice manufactured in these 

 machines. 



Moreover, it appears that the kind of freez- 

 ing-machines in question, which convert power 

 into cold, notwithstanding they are yet in 

 their infancy, have already attained such a de- 

 gree of excellence, that they are ahead of that 

 class of machines which convert heat into 

 power, either by steam, hot air, or any other 

 possible means, as it is proved that they pro- 

 duce the full theoretical equivalent of cold 

 (negative heat) for the number of foot-pounds 

 employed ; namely, cooling one pound of wa- 

 ter one degree for a power equivalent to 700 

 pounds descending one foot, which, expressed 

 in the adopted scientific manner, is one unit 

 of negative heat for every 700 foot-pounds 

 consumed. 



A New Chrome Green. M. Casthellaz has 

 discovered a process of making a chrome green, 

 said to be far more beautiful than any now in 

 use. He slowly preciptates chrome salts by 

 treating them with hydrated metallic oxides, 

 insoluble, or but slighly soluble in water, or by 

 hydrated metallic carbonates, or hydrated me- 

 tallic sulphides, or by salts of weak acids which 

 easily leave their bases. The action is produced 

 progressively, and the oxide, of chromium pre- 



cipitated in the hydrated forms. The color of 

 the compound is a magnificent emerald green. 

 A gelatinous alumina, oxide of zinc, carbo- 

 nate of zinc, and sulphide of zinc, are among 

 the reagents most economical to be used. The 

 same result may also be obtained by treating 

 chrome salts with non-alkaline metals, such as 

 iron and zinc. M. Casthellaz claims that the 

 superb green color produced by his method 

 possesses properties which will enable manu- 

 facturers ultimately to renounce the justly-con- 

 demned copper and arsenic greens, and he 

 looks for its adoption in oil-painting, colored 

 paper, and artificial-flower making, printing on 

 stuffs and on paper, lithography, perfumery 

 and soap manufacture, as well as in the mak- 

 ing of glass and in the ceramic arts. 



New Method of obtaining Oxygen. MM. 

 Montmagon and Delaire claim to have discov- 

 ered a new method of obtaining oxygen cheap- 

 ly and easily. They expose fresh wood char- 

 coal to atmospheric air, when it occludes the 

 oxygen and nitrogen of the air in certain pro- 

 portions. 100 litres of charcoal will occlude, 

 it is said, 925 litres of oxygen, but only 705 

 litres of nitrogen. The charcoal holding these 

 amounts of the two gases is then thoroughly 

 saturated with water, when there will be ex- 

 pelled 650 litres of nitrogen, but only 350 litres 

 of oxygen thus, there will be left in the 

 pores of the charcoal 575 litres of oxygen and 

 only 45 litres of nitrogen ; in other words, the 

 oxygen will be practically pure for industrial 

 purposes. To extract these remaining gases, 

 the authors employ a pump. By again allow- 

 ing the extracted gases to be exposed to fresh 

 charcoal, they obtain the oxygen nearly pure. 

 No cost of the process the all-important item 

 is given. 



Manufacture of Oxygen on the Large /Scale. 

 The works of the Oxygen Gas Company in West 

 Forty-first Street, New York City, are now in 

 full operation. The process of making oxygen 

 in their establishment is that invented by M. 

 Tessie du Motay, of France. M. du Motay's 

 object was to supply oxygen cheaply, and in 

 sufficient quantity for the practical introduc- 

 tion of the oxyhydrogen-light in place of the 

 common gaslight of Paris. The method of 

 manufacture may be briefly described as fol- 

 lows : A retort, of the kind ordinarily used in 

 gas-works, is partly filled with a manganate of 

 potash or soda, and heated to a cherry red. 

 Atmospheric air is then forced into it, at a 

 considerable pressure. The manganate, in its 

 heated condition, possesses the property of ab- 

 sorbing a large proportion of oxygen from the 

 air, and retaining it like a sponge. After an 

 exposure of about ten minutes to this opera- 

 tion, the air is then cut off, and steam is in- 

 jected into the retort at a high pressure. Pass- 

 ing through the manganate, the steam takes 

 up the oxygen left by the air, and carries it 

 into a condenser, where the steam is converted 

 to water again, while the oxygen passes off free 

 into a receiver. There are various stages of 



