42 
POPULAR SCIENCE REVIEW. 
buying, as agent for Queen Elizabeth, saltpetre, sulphur, and 
staves for making barrels. In the following century the parish 
register shows entries of deaths resulting from explosions at the 
mills ; and Fuller, who was rector of Waltham, alludes in one of 
his works to the dangers of the manufacture, remarking that 
the mills were blown up five times during the seven years of his 
residence in the parish. The only wonder is that explosions 
were not far more frequent in the old factories, where the elabo- 
rate precautions now adopted were utterly unknown. Powder 
was allowed to accumulate in heaps on the floor, spirits of wfine 
was used instead of water to moisten the ingredients, under the 
impression that it made better and stronger powder, and the 
drying process was effected by heating the powder on metal 
plates over a fire without any means of regulating the tempera- 
ture. Finally, all the workrooms were close together, and often 
under a single roof, so that if the powder in one room exploded, 
that in the rest would follow, like a boy’s train of crackers. 
It was in 1787 that Government bought the Waltham Mills 
from the last private proprietor, Mr. John Walton, supposed by 
some to have been a descendant of the family of old Izaak. 
Major (afterwards Sir William) Congreve was the first superin- 
tendent. Horse and water power only were employed, most of 
the machinery was of wood, and the incorporating mills were, 
like mortar-mills at the present time, worked only by horses. 
Since then great improvements have been introduced into the 
manufacturing process ; the factory has been widely extended, 
gun-metal and copper have been largely substituted for wood in 
the structure of the machines, refining-houses have been erected 
for purifying the saltpetre and sulphur, and retorts for preparing 
the charcoal. Machinery has been designed and erected for the 
preparation of the large cannon powder introduced of late years, 
and in the mills iron runners, driven by steam, have taken the 
place of the stone runners, drawn by old horses. A complete 
code of rules and precautions have been introduced, and every 
building protected by a system of lightning-conductors. The 
factory gives employment to about two hundred men, and can 
produce twenty-four thousand barrels of gunpowder in the year, 
and the powder is believed to be at once the best and cheapest 
made by any existing factory. 
Before describing the process of its manufacture at Waltham, 
it may be as well to note a few facts on its composition and 
action. Gunpowder may be regarded as a solid, which, by 
ignition, can be very rapidly converted into a large volume of 
gas at a high temperature. It is this quality which constitutes 
it an explosive, for the sudden expansion is what we call explo- 
sion, though the name is sometimes given to the loud report 
which accompanies it, caused by the outrush of the gas gene- 
