AVENTURINE 



277 



wheel, which works into a second similar wheel, 15, so as to turn it in a hori- 

 zontal direction. The pin, 16, of the last wheel works upon a two-armed lever, 19, 

 movable round the point h, and this lever moves the neck by means of the pin 17. 

 The shorter arm of the lever 19 has an oval aperture in which the pin 16 stands. As 

 soon as this, in consequence of the movement of the bevel -wheel 15, comes into the 

 dotted position, it pushes the oval ring outwards on its smaller diameter, and thereby 

 turns the lever upon the point h, into the oblique direction shown by the dotted 

 lines. The pin 16, having come on its way right opposite to its present position, sets 

 the lever again straight. Then the lever, by the further progress of the pin in its 

 circular path, is directed outwards to the opposite side; and, at last, when 15 has 

 made an entire revolution, it is quite straight. The longer arm of the lever follows, 

 of course, these alternating movements, so that it turns the neck upon its plate 10, by 

 means of the pin 17 : and, as 18 denotes the bill, this comes into the dotted position. 

 It may be remarked, in conclusion, that the drawing of fig. 100 represents about half 

 the size of which the automaton may be constructed, and that the body may be formed 

 of thin sheet copper or brass, 



In the former edition another example of an automaton was given, but it is thought 

 unnecessary to retain it. In many of the machines now employed, we have examples 

 of useful automata, superior in correctness of action to any of those which are at the 

 best only scientific toys. 



AUTOTYPE. See PHOTOGBAPHY. 



AVENA. A genus of corn-bearing grasses. The A. sativa is the common oat. 



AVENTURINE. (Aventurine, Fr.) A variety of quartz, which is minutely 

 spangled throughout with yellow scales of mica, is known as Aventurine quartz. It 

 is usually translucent, and of a grey, brown, or reddish-brown colour. There is also 

 an Aventurine felspar (Feldspath aventurine, Fr.), frequently termed sunstone (Pierre 

 de soleil); some lapidaries, however, calling this stone by the name of Aventurine 

 orientale. Aventurine quartz occurs at Capa de Gata, in Spain ; and the aventurine 

 felspar, or sunstone, at Tvedestrand, in Norway. 



AVENTUEINE, ARTIFICIAL, or GLASS, called also Gold Flux, has been manufactured 

 on a large scale, for a long period, at the glass-works of Murano, near Venice. 

 According to Wohlor's examination, aventurino glass owes its golden iridescence 

 to a crystalline separation of metallic copper from the mass coloured brown by the 

 peroxide of iron. C. Karsten analysed the artificial aventurine from the glass manu- 

 factory of Bigaglia, in Venice, and found it to contain 



These numbers agree in a remarkable manner with the results formerly obtained by 

 Peligot, and may therefore be regarded as truly representing the composition of the 

 glass. 



AvENTtJHiNE GLAZE, for porcelain, exhibits a crystalline separation of green oxide 

 of chromium from the brown ferruginous mass of the glaze producing a similar effect 

 to the glass. This glaze is prepared as follows, according to A. Wachter : 



31 parts of fine lixiviated dry porcelain-earth from Halle, 



43 dry quartz sand, 



14 gypsum, 



12 fragments of porcelain, 



are stirred up with 300 parts of water, and by repeated straining through a linen 

 sieve, uniformly suspended in it, and intimately mixed. To this paste are added, under 

 constant agitation, and one after the other, aqueous solutions of 



19 parts bichromate of potash, 

 100 protosulphate of iron, 

 47 acetate of lead, 



and then so much solution of ammonia that the iron is completely separated. The 



salts of potash and ammonia are removed by frequent decantation with spring water. 



The baked porcelain vessels are dipped into the pasty mixture obtained as above 



