152 



CHEMISTRY. 



Ozoufs Process for Carbonic Acid. This 

 process, described in a number (early part of 

 1865) of the Bulletin of the Society for the 

 Encouragement of Industry (Paris), consists 

 essentially in directing the gases, proceeding 

 from coke burnt in a specially constructed fur- 

 nace, and after the former have been properly 

 washed, through a series of vessels containing 

 solution of carbonate of soda ; the carbonic acid, 

 which is the principal constituent of the mixed 

 gas from the coke, is taken up by the carbonate, 

 converting it into the bicarbonate. The solution 

 so changed is then pumped into a cylinder, and 

 being heated to boiling-point, it parts with the 

 second equivalent of carbonic acid say, with 

 one-half the volume of this gas existing in com- 

 bination in it. The gas so disengaged should 

 be of course quite pure ; and it can be applied 

 to a variety of uses, as the manufacture of soda 

 and other effervescent waters, of white lead, 

 &c. The potash solution from which it has 

 been set free is ready for use over again. 



Ozoufs Process for White Lead. The report 

 just referred to, also describes the application 

 of carbonic acid, obtained in the manner given, 

 to the manufacture of white lead. M. Ozouf 's 

 process is in this respect substantially that of 

 Thenard, the passing of carbonic acid gas into 

 vessels containing solution of subacetate (basic 

 acetate) of lead. The inventor states, however, 

 that by proportioning the quantity of carbonic 

 acid gas to the composition of the subacetate, 

 the latter containing variable proportions of 

 acetic acid, from two down to only one of the 

 acid for every three equivalents of oxide of lead, 

 he is able to produce at will white lead of 

 any definite composition ; and this result is of 

 course one of practical importance. A sample 

 furnished by him, on analysis, showed a com- 

 position represented by the formula 3 (PbO, 

 CO,) + PbO, HO. 



Preparation of Potash. A brief note in the 

 Journal of the franklin Institute for Novem- 

 ber, 18G5, gives the substance of a mode of 

 procuring potash from feldspar. In this, feld- 

 spar, fluorspar, and chalk are pulverized, mixed, 

 and calcined. Floride of silicium is disengaged, 

 silicate of lime is formed, and potash is set free. 

 The alkali may be dissolved out with boiling 

 water, and freed from any lime carried with it 

 by carbonic acid. Some feldspars, however, 

 are said to contain large quantities of soda, and 

 on treatment to yield that base. 



Recent improvements in the manufacture of 

 soda and certain soda compounds, and in the 

 way of utilization of the waste of the works, 

 &c., are of sufficient interest to merit treatment 

 in a separate article. (See SODA AND SODA 

 COMPOUNDS.) 



Preparation of Nitre. The subject of nitrifi- 

 cation, or the production of the nitrate of pot- 

 ash in the so-called nitre-beds, natural and arti- 

 ficial, is considered under CHEMISTRY, volume 

 for 1862, and incidentally also in that for 1863. 

 Manufacturers of saltpetre have of late years 

 found it most advantageous to convert the cal- 



careous and magnesian nitrates (obtained by 

 leeching out of the nitre-yielding products of 

 the beds) into nitrate of soda, by means of sul- 

 phate of soda, and then, by chloride of potassium, 

 to convert the soda-salt into nitrate of potash 

 (Reguault). 



Still more recently, the fabrication of nitre 

 has been rendered more simple and less ex- 

 pensive by decomposing at the same time, and 

 without previous preparation, the chloride of 

 potassium and the sulphate of potash procured 

 from the salts of the sort of sea-weed known 

 as wrack, by reaction of nitrate of soda with 

 those salts. In the process, also, the slight 

 solubility at low temperature of the nitrate of 

 potash is turned to account, as well as its ready 

 purification by crystallization and washing ; and 

 the salts of less value remaining in the mother- 

 liquor are concentrated and dried for disposal to 

 manufacturers of glass. 



Preparation of Alum. Mr. Spence, England, 

 by making use of the schists which lie in con- 

 tact with beds of coal, has recently succeeded 

 in producing alum on a very economical scale. 

 Having roasted the schist in small heaps, by 

 aid of a little combustible matter along with 

 bituminous material contained in the former, 

 he treats the ash, reduced to powder, by sul- 

 phuric acid in the condition in which it comes 

 from the chambers. The excess of acid re- 

 quired for acting on the clay of the schist is 

 afterwards removed by saturating it in the fil- 

 tered solution by a current of ammonia directly 

 obtained from the ammoniacal waters of gas- 

 works. Five tons of the schist yield four tons 

 of alum ; while in case of the employment of 

 pyritous earths, a very much larger quantity of 

 the primary material is required to yield the 

 same result. Mr. Spence's works, in" which 

 this process is in use, turn out annually some 

 6,600 tons of alum, a quantity amounting to 

 one-third of that produced each year in the 

 whole of Great Britain. 



Detection of Explosive Gases in Mines. Of 

 the modes of testing whether or not explosive 

 gases are present in mines, by observing if a 

 peculiar form be given to the flame of a lighted 

 candle, or if a peculiar behavior or form be 

 presented by the flame of a Davy's lamp, the 

 former is exceedingly hazardous, while even 

 the latter is not free from the danger of origi- 

 nating explosion. Mr. G. F. Ansell, of the 

 Royal Mint, England, appears to have succeed- 

 ed in supplying the want of safe tests, in the 

 set of ingenious instruments recently devised 

 by him for the determination, and one of them 

 especially for he quantitative estimation, of the 

 presence in any atmosphere of explosive gases 

 or others different from those of common air. 

 All these are in their construction based on the 

 well-known principle that gases free to do so 

 mutually intermix, and that through porous 

 partitions, including many even of which the 

 porosity is not apparent ; and further, upon the 

 law that, in such cases, the gases diffuse into 

 each other with a rapidity inversely propor~ 



