CHEMISTRY. 



153 



tional to the square roots of their specific gravi- 

 ties ; so that the volume of a body of gas with- 

 in an enclosed space tends to he increased or 

 diminished at first, according as another gas 

 separated from it by a porous septum is rarer 

 or denser than itself. 



In the simplest form of the instruments re- 

 ferred to, a U-shaped tube, blown at one end 

 into a cup, has its bend filled with mercury so 

 that this occupies the lower part of the cup, 

 while over the latter is cemented a piece of 

 porous tile. The cup being thus chiefly filled 

 with air, inclosed, suppose it brought into an 

 atmosphere of hydrogen : the specific gravities 

 of the two are as (about) 14.4 and 1 ; the square 

 roots of these numbers, as 3.8 and 1 ; so that 

 for every 1 part of air diffusing out of the cup, 

 3.8 of hydrogen tend to enter it. In fact, 

 owing to the pressure thus generated within 

 the cup, effusion of gases goes on at the same 

 time ; but the former process being most rapid, 

 the mercury is depressed in the cup and raised 

 in the other arm of the tube. After the maxi- 

 mum effect of the diffusion is reached, effusion 

 still continues, until the two atmospheres have 

 come to a like constitution, and the mercury 

 has returned to the same level in both arms. 

 Upon then removing the instrument into com- 

 mon air, a reverse movement is set up, and the 

 mercury at first rises in the cup, falling in the 

 other arm of the siphon. But, placing the in- 

 strument, containing air, in carbonic acid (densi- 

 ties 14.4 and 22 ; square roots, 3.8 and 4.7), 

 the pressure is at first diminished in the cup ; 

 and the phenomena are throughout the reverse 

 of those just stated. As already implied, the 

 theoretical elevation or depression can in no 

 case be fully obtained ; but either is likely to 

 be of sensible amount. Alongside the smaller 

 arm of the U-tube is accordingly placed a scale; 

 and this is graduated to indicate the percentage 

 of mine-gas present. In other forms, a float on 

 the mercury in the smaller limb, connected 

 with a cord passing over a pulley, and a small 

 weight, moves an index over a circular scale, 

 for the like purpose. But while all these re- 

 quire to be directly watched, in a fifth form, a 

 small india-rubber balloon, allowed to expand 

 only in length, is made by its elongation on 

 taking through its pores a lighter gas, to act on 

 a lever, release clock-work, and thus ring a bell. 

 This instrument gives almost instant warning 

 of the sudden irruption of explosive gases into 

 a mine, and the bell continues to ring until by 

 ventilation the atmosphere of the place has re- 

 turned to its usual character. 



The most valuable of all these instruments 

 is, however, one resembling an aneroid barom- 

 eter, and of about the size of a watch, having 

 one of its faces of porous earthenware but ordi- 

 narily protected by a brass case, and an open- 

 ing through ite handle closed by turning a 

 screw. This being commonly open, so that the 

 cavity is filled with air, when an observation is 

 to be made the orifice is closed : taking the in- 

 strument into a mine, and opening the case, if 



the lighter mine-gases be present, in about forty- 

 five seconds their maximum effect will be pro- 

 duced ; and the position of the index will, by aid 

 of a vernier, show the percentage of mine-gases 

 present. Since trains of trucks running into or 

 out of the mine disturb the pressure, the instru- 

 ment should be used in the intervals between 

 such disturbances. It is stated that no appre- 

 ciable variation arises from temperature. Some 

 of the forms can be connected with telegraphic 

 arrangements. The instruments have been used 

 in several mines, and have given full satisfac- 

 tion to practical miners. Cuts of the instru- 

 ments accompany their description, in the 

 Chemical News, December 15, 1865. 



Applications of Bisulphide of Carbon. This 

 peculiar liquid (composition, CSj), an incidental 

 product of the distillation of coal, and which 

 has already received many interesting and valu- 

 able applications, has recently been applied 

 with great success to the extraction of fatty 

 matters from various seeds and fruits ; and also, 

 in Algiers, to the extracting from flowers of 

 various essential oils, commonly known as per- 

 fumes; as those of roses, lavender, jasmine, 

 &c. Messrs. Allbright & Co., of Binningham, 

 also use it to separate the common phos- 

 phorus from the red or amorphous phosphorus, 

 now applied to the manufacture of chemical 

 matches. 



Extraction of Vegetable Oils T>y means of 

 Volatile Hydrocarbons. It has recently been 

 found that all the more common vegetable oils, 

 including palm oil, olive oil, colza oil, and lin- 

 seed, rape-seed, and cotton-seed oils, may be 

 extracted with great economy by means of 

 some of the hydrocarbons from petroleum, coal, 

 schists, and bitumen, and best by those whicli 

 volatilize at a little above the boiling-point of 

 water. The seeds or fruits, crushed or ground 

 in the usual way, are digested with the hydro- 

 carbons in tight vessels. From the solution of 

 the vegetable oil in the mineral spirit which is 

 obtained, the latter is afterwards expelled by 

 applying a proper heat. The solvent is con- 

 densed for re-use, and the loss of it may be 

 made very slight ; while the yield of oil ob- 

 tained by the means indicated is said to be from 

 40 to 50 per cent, greater than that secured by 

 the ordinary method with mechanical press- 

 ure. It has been stated that, by employment 

 of this process, the yield of the olives pressed 

 yearly in the neighborhood of Marseilles alone 

 could be increased not less than 6,000,000 

 pounds. 



Preparation of Clay with Glycerine, for 

 Modelling. Experiments recently made byM. 

 Haas, of Stuttgard, confirm the opinion long 

 advanced as to the value of glycerine for pre- 

 serving the plasticity of clay intended for mod- 

 elling. He found that clay, kneaded up with 

 glycerine, and kept for two months in a warmed 

 room, was still as plastic as on the first day. 

 The clay should be first completely dried, then 

 pulverized, and finally mixed with the requisite 

 quantity of glycerine, of specific gravity of 



