Mechanical Science. 329 



oil is extinguished in air containing not more than 18. 1 per cent, 

 of oxygen, whilst naphtha and oil of bones burn when it contains 

 no more than 13.8 per cent. — Ann. des Mines, x. 64. 



4. Method of browning Iron. — Nitric acid, \ oz. ; sweet spirits 

 of nitre, i oz. ; spirits of wine, 1 oz. ; blue vitriol, 2 oz. ; tincture 

 of steel, 1 oz. These ingredients are to be mixed, the vitriol 

 having been previously dissolved in a sufficient quantity of water, 

 to make with the other ingredients one quart of mixture. Pre- 

 viously to commencing the operation of browning a gun-barrel, 

 it is necessary that it be well cleansed from all greasiness and 

 other impurities, and that a plug of wood be put into the muzzle, 

 and the vent well stopped. The mixture is then to be applied 

 with a clean sponge or rag, taking care that every part of the 

 barrel be covered with the mixture, which must then be exposed 

 to the air for twenty-four hours ; after which exposure the barrel 

 must be rubbed with a hard brush to remove the oxide from the 

 surface. 



This operation must be performed a second and a third time, if 

 requisite, by which the barrel will be made of a perfectly brown 

 colour. It must then be carefully brushed and wiped, and im- 

 mersed in boiling water, in which a quantity of alkaline matter 

 has been put, in order that the action of the acid upon the barrel 

 may be destroyed, and the impregnation of the water by the acid, 

 be neutralized. The barrel when taken from the water must 

 after being rendered perfectly dry, be rubbed smooth with a bur- 

 nisher of hard wood, and then heated to about the temperature of 

 boiling water ; it then will be ready to receive a varnish made of 

 the following materials : Spirits of wine, 1 quart ; dragons' blood, 

 pulverised, 3 drs. ; shell lac, bruised, 1 oz.''; and after the varnish 

 is perfectly dry upon the barrel, it must be rubbed with the bur- 

 nisher, to give it a smooth and glossy appearance. — SUlvnan's Jour, 

 ix. 168. 



5. Observations on Calcareous Cements. — The theory and im- 

 provement of calcareous cements have been taken up with much 

 interest in France, ^c, and we have at various times given 

 the results of MM. Vicat, John, and others. M. Vicat is opposed 

 in some of his theoretical conclusions by MM. John and Berthier, 

 and he has endeavoured to meet tlieir objections by reference to 

 facts and new experiments. Without entering into the discus- 

 sion, or endeavouring to convey to others a knowledge of its mi- 

 nute points, we shall take such facts as are brought to light at 

 different times, with the fair conclusions drawn from them ; con- 

 vinced in the highest degree of the importance of the subject, and 

 the advantage which the present investigations must lead to. 



M. Vicat states, that two kinds of sand were taken, one white 



