Chemistry and Physics. ' 1 1 



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dried, and then heated to redness, is considered to be oxyd of cobalt, 

 and part is sent in this state into the market ; anolher portion is heated 

 to a white-red ; by this treatment the oxyd loses in weight, but increases 

 in density ; it is sold as protoxyd of cobalt. The liquid from which 

 the cobalt has been precipitated is treated with milk of lime, which pre- 



^r cipitates the nickel in the state of hydrate ; this precipitate is washed, 



dried and heated to redness ; it is then mixed with charcoal, and by 

 means of a strong heat reduced to the state of a spongy nickel, which 

 is employed in the manufacture of German silver. With respect to 

 the oxyd of cobalt, nearly the whole of it is consumed in the Stafford- 

 shire potteries. The oxyd of cobalt thus prepared is remarkably pure. 

 15. On Liquid Protoxyd of Nitrogen; by M. Dumas, (Compt. 

 Rend., Nov. 6, 1848 ; Phil. Mag., xxxiv, 153, Feb., 1849.)— M. Nat- 

 terer of Vienna has constructed a forcing-pump for the liquefaction of 

 gases, by means of *vhich carbonic acid and protoxyd of nitrogen can 

 readily be obtained in the liquid state. Having procured one of these 

 instruments, and employed it more especially for the liquefaction of the 

 protoxyd of nitrogen, I soon perceived the necessity of using a series 

 of indispensable precautions, but which, once adopted, have enabled 

 me to effect with promptitude and security, as well as economy, the 

 liquefaction of large quantities of protoxyd of nitrogen. 



| As this liquid furnishes a means of producing an excessively low 



temperature, and is very easily operated with, I will here briefly point 

 out the observations I have made. The first relates to the principal 

 piece of the apparatus, that is to say, the reservoir. In my opinion the 

 Viennese manufacturer has not given it sufficient strength. 1 have had 

 it surrounded with a belt of forged iron, capable of resisting 800 atmos- 

 pheres, and very nicely made by M. Bianchi. Moreover, I have arranged 

 things so that the reservoir being surrounded by ice, the body of the 

 pump was cooled uninterruptedly by a circulation of water around it, 

 and that even the stem of the piston was always moistened by cold 

 w ater; in this manner there is no danger of the valve of the piston 

 being injured by the heat proceeding from the compressed gas, and by 

 ] *s special action as a combustible gas. With these precautions, we 

 may compress into the reservoir in the course of two hours 200 litres 

 of gas, of which 20 suffice to produce a pressure of 30 atmospheres, 

 about which, liquefaction commences. The remainder of the gas fur- 

 nishes a liquid ; 100 litres vield 200 grms., or very nearly. The gas 

 should be absolutely dry in order to succeed, and likewise as pure as 

 Possible. 1 prepare it from the nitrate of ammonia as usual, and after 

 having dried it, pass it into Macintosh bags; a couple of pounds of 

 nitrate of ammonia suffices. 



Once compressed, the liquid gas may be preserved for one or two 

 d *ys at least in tjie reservoir; the valve however is slightly injured by 



ll - When the stopcock of the reservoir is opened, the gas escapes; a 

 Portion freezes at first, but it then flows liquid ; the solid portion resem- 

 bles a mass of snow ; it melts upon the hand, and rapidly evaporates, 

 leaving a severe burn. The liquid portion, which is by far the most 

 abundant, and of which it is easy to obtain in one operation 40 to 50 

 S r ™s., being received in a elass, keeps for half an hour, or even more, 

 ^ the air. h 



Second Series, Vol. VIII, No. 22.— Jttty, 1849. 15 



