Now supposing the elements of gunpowder to exist in these proportions, it is essential, in order to secure their perfect combination, and thus to produce the largest possible volume of gas, that the elements should be in the most minute state of subdivision. Chemical action is a force exerted at insensible distances only, and chemical substances having the greatest affinity for each other will not combine, unless their elements are brought into immediate contact: thus oxygen and hydrogen may be mixed together in the exact proportions to form water; but no chemical combination will occur, simply because the ultimate particles of the two gases are not sufficiently near to each other for their chemical affinities to be brought into play; if, however, these gases are subjected to very strong pressure, so as to bring their particles into immediate contact, combination occurs, and the production of water is the result. In order to insure the perfect combination of the elements of gunpowder the same conditions are necessary; that is to say, the ultimate particles of the nitre, charcoal, and sulphur, must be brought into the most direct contact, or the explosive power of the gunpowder will be comparatively trifling. If, for instance, the nitre, charcoal, and sulphur be pounded in a mortar, no explosion but a slow combustion will occur when the mixture is ignited; so that unless this intimate mixture of the elements is carefully attended to in the manufacture of gunpowder, it is easy to see that the article produced will be of comparatively little value. It is evident then that if tons of the elements of gunpowder were stored in a warehouse which accidentally caught fire, no explosion would occur from the formation of gunpowder; though its ingredients would greatly increase the rapidity of combustion. This remark is elicited by the recollection of a fearful explosion which took place at Gateshead in 1854. It may be remembered that a warehouse caught fire from an adjoining mill, and the explosion was supposed to have been produced by the ignition of the elements of gunpowder stored in the warehouse in a crude state. The upper story of the building contained a large quantity of crude sulphur, and the basement story about the same quantity of nitre, whilst chemicals of various kinds were stored in other parts of the building; but according to the accounts published there was no large quantity of carbon in the warehouse; nevertheless, a terrific explosion took place, and after a lengthened investigation, the conclusion arrived at was this: the sulphur melting, mixed with the nitre, gunpowder was thus formed, and igniting, exploded, producing the terrible effects. But gunpowder may be made without sulphur, whereas gunpowder without carbon is an impossibility; and though the elements of gunpowder had all been present, no explosion could have occurred, unless they had become mixed in the intimate manner already described.