The powder thus separated into grains is still damp and full of dust. To get rid of this it is taken by water to the dusting-house, where it is bolted in a reel like so much flour. It has now to be glazed, a very important operation, performed by placing it in large barrels, which revolve with their load thirty-two times a minute for three hours together. By the mere friction of the grains against each other and the sides of the barrel, a fine polish is imparted to the surface of the grain, which enables it to withstand the action of the atmosphere much better than when it is left unglazed. It is now stoved for sixteen hours in a drying-room heated by steam pipes to a heat of 130° Fahrenheit, and is then finally dusted and proved. There are many methods of proving, but the simplest and most efficacious is to fire the powder from the weapon it is intended to serve. Thus cannon powder is proved by firing a 68-pound solid shot with a charge of two ounces of powder--a charge which should give a range of from 270 to 300 feet. If the powder passes the test, which it generally does, it is packed in barrels holding 100 lbs. each, marked L. G. (Large Grain), and F. G. (Fine Grain), as the case may be, and carried to the provisional magazine. When 500 barrels have accumulated they are despatched in a barge to the Government magazine at Purfleet, near the mouth of the Thames, the Lea forming the connecting link of water between the canals of the works and that river. The produce of this establishment, which had fallen so low as 4,500 barrels per annum in 1843, is now so increased by improved machinery that 20,000 barrels a year can be manufactured, and of the very best quality. Even this supply is far below the consumption during a time of war, and contractors have, and always will have, to furnish a portion of the required supplies; but it seems that a model mill is useful for the double purpose of keeping up a due standard of quality,[27] and of keeping down price. On the uniform strength of the powder depends the accuracy of artillery fire: hence the necessity of having some known standard of quality from which contractors should not be allowed to depart. The improvements which have taken place in the manufacture are very marked. About the year 1790, when powder was supplied to Government wholly by contract, the regulation weight of charge for a cannon was half the weight of the ball; it is now less than one-third: therefore two barrels are now used instead of three, a reduction of bulk which economizes stowage on board ship as well as in the field. Formerly powder had a range of 190 feet only; the range is now increased to 268 feet! This vast improvement is simply the consequence of the care with which the powder is worked, and the attention bestowed on every detail of the mills since their direction fell into the hands of Colonel Tulloh, Colonel Dickson, and Colonel Askwith, the present Superintendent.