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THE POPULAR SCIENCE MONTHLY. 



The drying-house is a large room with double doors, and fitted with 

 racks from floor to ceiling. On these racks copper and wooden trays 

 are placed, containing the powder, spread out in thin layers. Steam- 

 pipes are introduced from a boiler in an adjoining building, and thus 

 the air of the room is kept at a temperature of about 135. The fire- 

 men in charge of the drying are forbidden to enter the room for fear 

 of carrying in a spark in their clothes, but they ascertain the tempera- 

 ture by a register thermometer placed inside a small window, and this 

 thermometer also acts as a telltale, by showing if the temperature has 

 at any time been allowed to become too high or too low. So perfect 

 are all the arrangements at Waltham, that no explosion has ever oc- 

 curred in the drying-house. 



The dried pebbles are finished by being placed in a revolving bar- 

 rel (called a glazing-barrel), with a certain amount of powdered black- 

 lead. On being taken out, every pebble is found to have a perfectly 

 smooth surface coated with black-lead, the effect of wfyich is still fur- 

 ther to diminish the rate of burning. The pebbles are then thrown 

 into sieves to separate small fragments ; all irregular pieces are picked 

 out by hand, and the remainder is packed in ordinary powder-barrels, 

 which would hold 100 pounds of rifle-powder, but contain 125 pounds 

 of the pebble-powder, on account of its greater density. 



The following results of experiments with the 8-inch gun will give 

 the reader an idea of the effects of the different kinds of powder. We 

 need only explain that R. L. G. means the old "Rifle Large Grain" 

 powder, still in use for field-artillery, and draw attention to the fact 

 that the pebble-powder gives at once the highest velocity and the 

 lowest strain : 



Visitors to the laboratory at Waltham can see tbere a number of 

 experimental varieties of pebble-powder, the largest of which consists 

 of cubes as hard as stone, each side of which is two inches square. A 

 shower of this alone fired from a gun would be quite as effective as 

 grape, and it is possible that 300 pounds of this tremendous powder 

 will form the charge of the new 80-ton gun. 



For rifle-powder the meal is pressed into thin cakes ; these are 

 broken up into irregular pieces by hand, and carried to the granulating 

 machine. This machine consists of four pairs of toothed cylinders, 

 between which the broken cake is passed. As it falls from them in 

 grains, it is received upon a series of screens of net-work. There are 





