Progress of Invention. 237 



changes them very quickly to red, without, however, diminishing 

 their brilliancy or transparency. That, in becoming red, the phos- 

 phorus has not changed its properties is evident from the fact that 

 if heat is again applied, it will be covered with the white crystals. 

 The latter, as might be expected from the eminently electro -positive 

 properties of the phosphorus, rival the diamond in brilliancy. 



I Simplification of the Soda Manufacture. — Sulphide of sodium, 

 is, in the ordinary process of manufacture, changed into sulphate 

 of soda, by means of nitrate of soda, which involves considerable 

 expense. It has been found, however, that the oxidation of the 

 sulphide may be effected by far less costly means. For this pur- 

 pose it is only necessary to utilize the oxygen of the air, which is 

 effected in the following way : — The crude liquor is placed in a vessel 

 with a false bottom, having a great number of small holes. Into 

 the centre of this false bottom has been inserted a pipe, the upper end 

 of which projects over the top of the vessel, and terminates above 

 by a funnel-shaped throat. Steam of about forty pounds pressure 

 being made to issue from a jet, which is situated a little above the 

 throat, in rushing into the funnel it carries along with it a large quan- 

 tity of air : and this issuing through the holes of the false-bottom, and 

 passing into the fluid in a finely-divided state, so as to come in con- 

 tact with a very large surface, all the oxidisable matters present are 

 oxidized, and thus a considerable quantity of sulphite is changed 

 into sulphate in a very short time. The manufacture of alkalies is 

 carried on at present on so vast a scale that any improvement of 

 the processes used in it must be productive of an immense saving. 



Improvement of Glass for Optical Purposes. — Great refrac- 

 tive power is the chief desideratum in glass for optical purposes. 

 This is obtained by means of great density, which hitherto has been 

 due to lead. It has been found, however, that replacing the potash 

 or lead, and especially the former, with thallium, affords a highly 

 refractive glass of the finest description. 300 parts sand, 200 parts 

 peroxide of lead, and 335 parts carbonate of thallium give a glass 

 which has a greater specific gravity and a higher refracting power 

 than any other known, its specific gravity being 4*235, and its index 

 of refraction for the yellow rays, T71. It is perfectly homogene- 

 ous, and has a slight yellow shade which is very pleasing. It may, 

 perhaps, be found useful to makers of artificial gems. A much 

 greater specific gravity and higher refractive power may be attained 

 by altering the relative amounts of the ingredients. 



ISTew Electric Alarm. — An electric alarm of extreme delicacy, 

 the invention of M. Robert Houdin, is formed by soldering together 

 a blade of copper and another of steel, fixing one end of this com- 

 pound blade to a board, along which it lies parallel, something after 

 the manner of a knife used in chopping, but not in contact, that 

 friction may be avoided. Near the free extremity of the blade is a 

 metallic knob, which is capable of being moved to different dis- 

 tances from it, and is in conducting communication with one pole 

 of a galvanic battery, the free end of the compound blade being 

 in connection with the other. When the temperature of the 

 surrounding air is increased, the compound blade becomes carved, 



