471 



enlarged laterally to about double the size of the other teeth ; so that at the completion 

 of every revolution of the wheel the projecting tooth shall act upon a tooth of the 

 next disc, and carry that disc forward one-tenth of a revolution. By this means the 

 requisite movements of the discs for effecting the regular progression of the numbers 

 are produced ; the first wheel driving its own disc, and communicating motion at in- 

 tervals to the next disc, and the other wheels each receiving motion at intervals from 

 the disc with which it is connected, and transmitting motion, at still greater intervals 

 of time, to the next disc. 



The machine is caused to print the figures in duplicate by drawing the spring catch 

 out of action at every alternate descent of the frame, and thereby preventing any change 

 of the figures taking place until after the next impression. 



The numbers may be increased two units at each impression, so as to print all even 

 or all odd numbers, by bringing a second catch into action, which causes the unit disc 

 to advance one step during the ascending movement of the frame, in addition to the 

 advance during the descent of the same. 



PAKJTS are colouring-matters in combination with oil. In most cases for the 

 ordinary paints the basis is white lead, with the colouring agents derived from the 

 mineral or vegetable kingdom mixed with it. This does not apply to artists' colours 

 (see COLOURS). The advantages of lead are, that its carbonate (or white lead) 

 actually combines with the oil, whereas white zinc is merely mechanically suspended 

 in it. In the one case we have a plaster spread over the wood or canvas to which 

 the paint is applied, in the other we have only a fine powder held by the oil so long 

 as it continues permanent, but which washes out when the oily coating begins to givo 

 way. 



Oxide of zinc, or white zinc, is, however, much used as a paint. Ground with oil, it 

 docs not cover the surface of wood so well as a lead paint does, owing to the condition 

 in which it exists, as already explained. It has, however, one advantage over white 

 load, as it is not liable to tarnish or blacken when exposed to the action of sulphide 

 of hydrogen. It has been stated that white zinc is not injurioiis, as white lead is, to 

 the health of the painter. This is very questionable. It has been found that the long- 

 continued use of whito zinc paint produces a distressing nausea. 



A white paint has been made from the oxide of bismuth ; but the metal is too scarce 

 to make it an article of commercial value. A tungsten white was made in tolerably 

 large quantities a few years since, and it was advertised as possessing many advantages ; 

 as it has not maintained its ground, we may therefore suppose that the promises were 

 not fulfilled. 



Copper is largely used as a paint. The most brilliant greens are compounds of the 

 oxide of this metal with arsenic and other bodies. There are also several blues of 

 great value produced from copper. 



Iron. The oxides of iron, in various forms, are employed in the production of 

 yellow, brown, and black paints. A very beautiful black is produced by calcining 

 with care spathic iron ore, the white carbonate of iron ; the result is a black magnetic 

 oxide, which mixes well with oil, and forms a most permanent covering for out-of-door 

 work. Calcined hsematitic iron ores are also found to produce most permanent 

 colours, which resist the action of the weather in a remarkable manner. 



Anthracite, ground to an impalpable, powder, has been extensively used, when 

 mixed with a drying oil as a black paint. A considerable quantity of this paint was 

 manufactured at Bideford, in North Devon, where the anthracite is obtained from the 

 well-known culm measures of that district. Nearly all paints employed by the 

 ordinary house-painter should be, however, lead paints to which colour has been 

 imparted by the use of some of the metallic oxides. For artists' paints, see COLOURS ; 

 LEAD, OXICHLOEIDE ; and WHITE LEAD. 



PAINTS, GRinDIKTG OI". Thero are many pigments, such as common orpi- 

 ment, or king's yellow, and verdigris, which are strong poisons ; others which are 

 very deleterious, and occasion dreadful maladies, such as white lead, red lead, chrome 

 yellow, and vermilion ; none of which can be safely ground by hand with the slab 

 and muller, but should always be triturated in a mill. The emanations of white lead 

 cause, first, that dangerous disease the colica pictonum, afterwards paralysis, or 

 premature decrepitude and lingering death. 



Figs. 1583, 1584, and 1585 exhibit the construction of a good colour-mill in three 

 views: jig. 1583 being an elevation shown iipon the side of the handle, or where the 

 power is applied to the shaft ; fig. 1584 a second elevation, taken upon the side of the 

 lino od of the plan or bird's-eye view, fig. 1585. 



The frame-work A A of the mill is made of wood or cast-iron, strongly mortised or 

 bolted together, and strengthened by the two cross iron bars BB. Fig. 1586 is a plan 

 of the millstones. The lying or nether millstone c, fig. 1584, is of cast iron, and is 

 channelled on its upper faco by corn millstones. It is fixed upon the two iron bars 



