That it is not generally adopted is owing to its containing a large proportion of that seemingly dangerous substance, nitro-glycerine, which makes the handling of dynamite a somewhat hazardous operation. According to Professor Abel, there are now as many as fifteen dynamite factories in different parts of the world (including a very extensive one in Scotland) working under the supervision of Mr. Nobel, the originator of the nitro-glycerine industry; and six or seven other establishments exist where dynamite or preparations of very similar character are also manufactured. The total production of dynamite in 1867 was only eleven tons, while in 1878 it amounted to 6140 tons. This explosive compound is most extensively used for general blasting purposes all over the world, and for this purpose, owing to its cheapness and the convenience in manipulating it, is far superior to compressed gun-cotton. Gun-cotton is formed by the action of concentrated nitric acid on cotton, its composition being indicated by the formula _CH_{7}(NO_{2})_{3}O_{5}_. Professor Abel's process for manufacturing pulped and compressed gun-cotton is as follows:-- Cotton waste is the form of cotton used; it is picked and cleaned, thoroughly dried at 160° F., and then allowed to cool. The strongest nitric and sulphuric acids are employed, mixed in the proportion of one part of the former to three of the latter by weight. These are mixed in large quantities, and stored in cast-iron tanks. The cotton in 1-lb. charges is immersed in the acid mixture, which is contained in a trough surrounded by cold water. After being subjected to the action of the acid for a short space of time, the cotton is taken up, placed upon a perforated shelf, and as much as possible of the acid squeezed out of it. It is then put into jars, covered with fresh acid, and the jars placed in fresh water, remaining there for twenty-four hours. To remove the acid, the gun-cotton from the jars is thrown into a centrifugal strainer, by which nearly all the acid is expelled. It is then diffused quickly in small quantities through a large volume of water, and again passed through a centrifugal machine. The next process is that of thoroughly washing the gun-cotton, for the purpose of removing the traces of the acid still adhering to it. By pulping, which operation is performed in pulping engines or beaters, the washing is expeditious and thorough. A _beater_ is an oblong tub in which is placed a revolving wheel carrying strips of steel on its circumference. From the bottom under the wheel project similar steel strips. The action of this machine is as follows:-- By the rotation of the wheel, the gun-cotton which is suspended in water circulates around the tub, and is drawn between the two sets of steel projections, by which it is reduced to a state of _pulp_. The bottom of the tub is movable, and thus the space through which the gun-cotton must pass may be contracted, as the operation proceeds.