666 



PRUSSIAN BLUE 



lye. Campheno may be substituted for oil ; but owing to its combustible nature il is 

 objectionable, as accidents may arise from its use. 



PRINTING, STEREOTYPE. See STEREOTYPE. 



PROOF SPIRIT. See ALCOHOL. 



PROPYXiENE. A gas obtained among the products of the decomposition of 

 amylic alcohol. See GASCOAI 



PROTEINE. The name given to the substance obtained by digesting albuminous 

 matters in weak caustic potash, and precipitating by acetic acid. 



PROTOGINE (irpGiTos, first ; ylyvofuu, to form). A granite composed of felspar, 

 quartz, and talc. This term is nearly restricted to the French geologists. 



PROUSTITE, or Light Bed Silver Ore. An arsenic-sulphide of silver, resembling 

 pyrargyrite, but distinguished by its paler cochineal-red colour. It is a valuable ore, 

 found in Saxony, Mexico, Chili, Nevada, &c. See SILVER. 



PROVING IVIACHINE. The figures show a useful machine for testing the 

 quality and power of india-rubber springs, designed by Mr. George Spencer, of the 



firm of Geo. Spencer and Co., and used by them for that purpose. Fig. 1692 shows 

 an elevation, partly in section, of the machine: Jig. 1693 a plan of the same. A is 

 a strong cast-iron frame, supported by two cast-iron standards, B, B ; c is a sliding 

 piston, working in a hole cast in the end of frame, A, one end of which impinges 

 against the short arm of a strong cast-iron lever, D, forming one of a system of com- 

 pound levers as shown, having fulcrums at F and /, and provided with a Salter's 

 balance, g, to register the power exerted by the spring. 



At the other end of frame, A, a brass nut, o, is placed in a hole in the frame, 

 through which a square-threaded screw, s, works by means of the handle, H, or by a 

 long lover of wrought iron, according to the power of spring to be tested. 



The spring to be tested is placed between the two sliding guide-plates, N, N', and 

 a wrought-iron bolt passed through the plates, N, N', and spring, z, and passing into 

 the hollow piston, c, for the purpose of keeping the spring in correct position, and 

 receiving in its hollow head, M, the end of the screw, s. The action may bo thus de- 

 scribed : The handle, H, being turned, the screw, s, advances and pushes on the plate 

 N 7 , by means of the bolt-head, M. The other plate, N, rests against the piston, c, and 

 is pressed against it by the intervening spring, z. The leverage, D, is so arranged 

 that 1- Ib. on the dial is equal to 2 cwts. on the spring, or, in other words, is 1 in 224. 

 Springs of a force of 20 tons can be tested by this machine safely. See CAOUTCHOUC. 



PROVISION'S, CURING OP. See MEATS, PRESERVED ; PUTREFACTION. 



PRtTNEIiIiA. A thin woollen or mixed stuff now chiefly used for covering 

 shoes, especially such as are worn by old women. 



PRTTNUS. A genus of the Rosacca, containing several species which yield edible 

 fruits. The varieties of P. domestica are known as plums, greengages, and damsons. P. 

 cerasus is the cherry ; P. Armeniaca the apricot ; and P. spinosa the sloe or blackthorn. 



PRUSSIAN 1 BI.UE. (Berliner Blav, Ger.) This is, in its pure state, a ferro- 

 cyanide of iron (ferric-ferrocyanide). When organic matters abounding in nitrogen, 

 smell as dried blood, horns, hair, skins, or hoofs of animals, arc triturated along with 





