MECHANICS AND USEFUL ARTS. 105 



Time for tanning in Time for tanning in 



vacuo without motion. barrel, when rotated. 



Calf-skins, from .... 6 to 11 days 4 to 7 days 



Horse-hides, 35 to 40 " . . . . 14 to 18 " 



Light cow-hides, . . . 30 to 35 " . . . . 12 to 13 " 



Cow-hides, middling, . . . 40 to 45 " . . . . 18 to 20 " 



Heavy cow-hides, . . . . 50 to 60 " . . . . 22 to 30 " 



Ox-hides, light and middling, . 50 to 60 " . . . .20 to 3D " 



Ox-hides, first quality, . . . 70 to 90 " . . . &> to 40 " 



At the same time, 75 per cent, of bark is saved by using the rotary barrel. 



PREPARATION OF FRICTION MATCHES. 



"Wagner has published the following results of his investigations respecting 

 the preparation of friction matches. 



The ingredients used are phosphorus, a metallic oxide, nitre, and a cement- 

 ing substance. One of the most important points in the preparation of the 

 paste is the proportion of phosphorus. This should not be more than one- 

 tenth or one-twelfth, when the phosphorus is melted in solution of gelatine, 

 after the usual method. A much smaller amount of phosphorus is sufficient 

 for the preparation of a good paste when the mode of preparation is altered. 

 A greater effect is produced with a given quantity of phosphorus when it is 

 very finely divided, on account of its greater inflammability in this state. A 

 solution of phosphorus in bisulphide of carbon, leaves the phosphorus so 

 finely divided on evaporation, that it ignites by contact with the air. How- 

 ever, when this finely divided phosphorus is mixed with solution of gelatine, 

 the dry mass does not ignite when exposed to the air, although it is very in- 

 flammable. Apart from greater expense of a large amount of phosphorus, it 

 is otherwise disadvantageous, owing to the production of a film of phos- 

 phoric acid, which renders the ignition of the wood or stcarine more difficult. 



Wagner recommends the following mode of preparation : 



Eight parts phosphorus dissolved in bisulphide of carbon; 21 parts gelatine; 

 24 parts peroxide of lead, and 24 parts nitre. 



He considers that the binoxide of manganese would be the best adapted to 

 the preparation of the paste, since it contains a larger amount of oxygen than 

 red lead or peroxide of lead, and as the metallic oxide serves only to main- 

 tain the combustion by yielding oxygen. 



The nitre also is supposed to be serviceable only as a source of oxygen, 

 and might therefore be replaced by some other nitrate; for instance, nitrate 

 baryta, which, like the potash salt, is anhydrous. The amorphous phos- 

 phorus does not seem to be nearly so good for the preparation of matches as 

 ordinary phosphorus, most likely in consequence of the necessity for the 

 conversion of amorphous phosphorus into ordinary phosphorus before igni- 

 tion takes place. 



M. Canouil, of Paris, has patented the following mixtures without phos- 

 phorus for the manufacture of matches : 



1. Dextrine (British gum), 10 parts. 



Chlorate of potassa, 75 " 



Brown oxide of lead, 85 " 



Iron-pyrites, 35 " 



Water, q. s., . 



The chlorate, binoxide of lead, and pyrites are powdered separately, and 



