proceedings of the polytechnic association. 455 



Soda Salts. 



The reactions wliicli take place in the celebrated process of Leblanc for 

 manufacturing' soda have never been fully and satisfactorily explained. M. 

 Scheurin Keshner now states that the reactions in the formation of black 

 ash or impure carbonate of soda, pass through three phases. In the first, 

 sulphate of soda is reduced to sulphide of sodium, carbonic acid being 

 given oil' — 10 atoms of sulphate and 20 of carbon, giving 10 of the sulphide 

 and 20 of carbonic acid; then a double decomposition takes place between 

 the sulphide of sodium and carbonate of lime; and lastly a partial decom- 

 position of the carbonate of lime employed iu excess is effected by carbon, 

 carbonic oxide being- disengaged. Tliis reduction is arrested by the cool- 

 ing of the mass. The quantity of carbon required is nearly 20 to 100 

 parts of sulphate of sodium, but an addition of excess of chalk is a,lways 

 desirable. 



Crystalline Pictures. 



M. Kuhlman, in a communication to the French Academy, refers to the 

 crj'stalization on glass of saline solutions thickened with gum. Barbers 

 and others ornament their windows by the use of sulphate of magnesia, 

 but the most beautiful effects are obtained twith the sulphate of zinc, and 

 the appearance, is improved bj'' painting over the crystalization with an 

 alcoholic solution of some coloring matter such as fuchsine. As these pic- 

 tures are very instable he has applied photography in copying them. He 

 also tried the galvano-plastic method for reproducing them so as to be able 

 to print them on paper or fabrics. He obtained the crystalization upon a 

 thin plate of copper, and copied it by pressing this plate on another by 

 means of powerful rollers. He suggests pressing gutta percha on glass 

 plates covered with crystals and electrotyping the mold. He exhibited 

 also a specimen of ornamentation iu gold and silver which is proposed as a 

 substitute for the ordinary chasing used on ornaments made of these metals. 

 The author stated that no two crystalizations were precisely alike. They 

 can only be copied by photography, for the fineness of the designs would 

 defy the burin of the most skillful engraver. He therefore proposes that 

 designs obtained in the waj- described on copper plates be used for bank 

 notes. If printed with pale blue' ink on a bright yellow ground, the photo- 

 grapher and the engraver would both fail to produce a counterfeit. 



An Iron Letter. 



The Birmingham (England) Journal announces the reception of a letter 

 by the last American mail, remarkable both as a documentary curiosity, 

 and as a specimen of manufacturing skill. It is written on iron rolled so 

 thin that the sheet is onl}- twice the weight of a similar sheet of ordinary 

 note paper. The letter is dated " South Pittsburg (Pennsylvania), Novem- 

 ber 6, 1864," and says: "In the number of your paper dated October 1, 

 J 864, there is an article setting forth that John Brown & Co., of the Atlas 

 Works, iSlieflield, had succeded in rolling a plate of iron 13| inches thick. 

 I believe that to be the thickest plate ever rolled. I send you this speci- 

 men of iron made at the Sligo Ironworks, Pittsburg, Pennsylvania, as the 

 thinnest iron ever rolled in the world up to this time, which iron I challenge 



