MANUFACTURE, ETC., OF GUNPOWDER. 723 



The first process is that of simply mixing the ingredients. For 

 this purpose the proper quantities of each are accurately weighed out, 

 allowance being made for a certain amount of moisture in the salt- 

 petre. The proportions vary in different countries, and according to 

 the purpose for which the gunpowder is to he used. For English 

 Government powder of every kind it is saltpetre 15 parts, sulphur 

 10, charcoal 15, the sulphur being reduced almost to a minimum, as 

 its chief use is only to ignite the charge and accelerate its action. In 

 France and Prussia the quantity of sulphur is larger, the scale being 

 saltpetre 75 and 12.5 parts each of sulphur and charcoal, while in 

 Chinese powder the amount of sulphur is between 14 and 15. It is 

 remarkable that in all countries the proportion of saltpetre remains 

 about the same. 



The ingredients, being weighed for a charge of 50 pounds, are poured 

 into a " churn." This is a revolving drum, placed horizontally, and 

 having within it an axis revolving in a different direction from the 

 drum, and furnished with eight rows of projecting arms, or " fliers." 

 So rapid is the action of this apparatus, that when the charge has heen 

 three minutes in the revolving churn the ingredients are thoroughly 

 mixed together. It is then known as a " green charge," and is ready 

 for the incorporating mills, the object of which, as the name indicates, 

 is to incorporate the materials, or to make the mixture so intimate 

 that a new substance is produced, namely gunpowder. 



The incorporating-houses at Waltham contain at present thirty-two 

 separate mills. Each mill consists of a pair of runners, coupled to- 

 gether by a strong axle. This axle rests in the socket of an upright 

 shaft, which, passing down through the mill-bed, is connected by 

 bevel-wheels with a revolving horizontal shaft, driven by steam or 

 water-power. The runners are either of black Derbyshire limestone 

 or of iron, and weigh from three and a half to four tons. Iron runners 

 are now generally used, and their size varies from three and a half to 

 seven feet in diameter. The mill-bed, a large circular vat with a flat 

 bottom and sloping sides, is of stone or metal, according to the ma- 

 terial of the runners. On this bed 50 pounds of the green charge is 

 spread out and moistened with water, and the mill is then set going. 

 The length of time required for the incorporation of the powder varies 

 according to the use to which it is to be applied. Thus cannonqww- 

 der is left under the mills for three hours; while for rifle-powder, 

 which requires a closer incorporation on account of its more rapid 

 action, the time is five hours. The power of a gunpowder-factory is 

 measured by the number of pairs of runners it possesses, for, as the 

 law allows no more than 50 pounds to be placed in any mill at one time, 

 the amount which can be incorporated in a year is easily calculated. 

 A pair of iron runners, driven by steam and working day and night, 

 will incorporate in a year nearly 100,000 pounds of cannon-powder, or 

 about half that quantity of rifle-powder. 



