Page:The American Cyclopædia (1879) Volume XVI.djvu/107

 TYPE-SETTING MACHINE of elements. 2. When this substitution takes place in equal numbers of equivalents, the body in which the substitution occurs retains its chemical type, and the elements which have entered into it play therein the same part as the element which has been abstracted. The chemical type included bodies containing the same number of atoms of their elements, and resembling each other in their principal chemi- cal properties, such as chloroform, bromof orm, and iodoform. But when the number of ele- ments varied while the number of atoms of the substance remained the same, they were re- garded as belonging to the same molecular type, as marsh gas, CH 4, formic acid, CHaOa, chlo- . roform, CHC1 3, and chloride of carbon, CC14. Berzelius opposed this theory, holding that acetic acid and trichloroacetic acid, which Du- mas regarded as belonging to the same type, did not so belong, but that acetic acid is an oxide of a radical, while trichloroacetic acid consists of oxalic acid copulated with chloride of carbon ; and so of other substitution com- pounds. But to maintain this position it was necessary to invent many radicals for com- pounds which were evidently analogous; and therefore when Melsens showed that acetic can be produced from trichloroacetic acid by the action of sodium amalgam, the idea that these two bodies were not built upon the same type could no longer be maintained. Gerhardt, by the introduction of his " theory of residues," reconciled the radical and substitution or type theories by supposing that a radical can be substituted for an element in a compound without altering the type ; not, however, by direct substitution, but by the formation of a body of elements from each of the bodies brought together, by which residues are form- ed that subsequently unite. The discovery of the alcoholic ammonia bases by Wurtz and Hof- mann in 1850, by which it was shown that the hydrogen in ammonia, NH 3, may be replaced by equivalents of the radicals ethyle and me- thyle, favored the union of the two theories. This conclusion was still further strengthened in the same year by Williamson's explanation of the general relations of the ethers and al- cohols by referring them to the type of water, H a O. Four principal types are now recog- nized, which are illustrated by the union of one, two, three, and four molecules of a mon- atomic element respectively with another mo- nad, dyad, triad, or tetrad, as HH, OH S, NH 8 , CH 4 ; and nearly all organic compounds may be regarded as formed by a combination of two or more of these types. The same compound may often be referred to different types. Thus, trichloride of phosphorus, PC1 3, maybe formed from three molecules of hydrochloric acid, 3H01, by the substitution of one molecule of the triad phosphorus for three hydrogen mo- nads ; or from one molecule of ammonia, NH 3 , by the equivalent substitution of phosphorus for hydrogen. TYPE-SETTING MACHINE. See FEINTING. 803 VOL. xvi. 7 TYPE WRITERS 95 TYPE WRITERS, mechanical contrivances for writing or printing with a system of movable types instead of a pen. They involve : 1, a po- sition movement, for bringing type to a print- ing point ; 2, an inking device ; 3, an impres- sion movement ; and 4, a device for letter and line spacing. These elements have been com- bined in a variety of ways. The most primi- tive is that in which the types are engraved on a cylindrical bar, which bar is revolved on its axis and also moved backward or forward by the hand of the operator, to present the desired type to the common printing point. This bar is then depressed, thereby delivering the impression through a saturated ribbon upon a sheet of paper wrapped around a cylinder placed at right angles with the type-carrying impression bar. To the paper cylinder a ro- tary and a longitudinal movement are impart- ed for the purpose of accomplishing the letter and line space. Nearly the reverse of this is the machine in which the types are arranged on a sliding rod or a narrow bed, and the im- pression is given by a bar or lever, the impres- sion point of which is equal in size to the face of a letter. This machine was designed to form wax matrices for stereotype moulds, but can be used for printing by interposing paper and inking ribbon between the type and the im- pression bar. A combination of the essential elements of these two machines was patented in the United States in 1868, the types being arranged on a plate in parallel rows, and the impression given by a plunger or striker. All necessary movements in this machine are ac- complished by mechanical means, the operator being simply required to move or depress a key corresponding to the letter desired to be printed. Another class of type writers may be generally described as consisting of a letter wheel or disk, on the periphery of which the types are engraved, which type wheel is re- volved on its axis for the purpose of presenting the desired letter to the printing point, after which either paper or wheel is moved to give the impression. Another method of type wri- ting is by means of a section of a globe or hemi- sphere, having a series of perforations from circumference to centre, in which are placed sliding plungers. On the inner end of each plunger is engraved a type, and on the outer end, upon a button or knob, the corresponding letter. These plungers are directed toward a common centre or printing point, and the pa- per is fed past this point to produce the letter and line space. The principal mechanical de- vice of another type-writing machine consists of an arrangement of key levers of varying lengths, which levers are made to pass each other and present their type-bearing ends at a common printing point. The Sholes andGlid- den type writer consists of a series of swing- ing type bars of equal length, pivoted on the circumference of a circle, in such manner that their type-bearing ends, when brought to the printing point, will strike at the centre of the