PYRITES 673 



Preserving with vinegar, sugar, $c. Vinegar dissolves or coagulates the albumen of 

 flesh, and thereby counteracts its putrescence. The meat should be washed, dried, 

 and then laid in strong vinegar. Or it may be boiled in the vinegar, allowed to cool 

 in it, and then set aside in a cold cellar, where it will keep sound for several months. 



Fresh meat may be kept for some months in water deprived of its air. If we 

 strew on the bottom of a vessel a mixture of iron-filings and flowers of sulphur, and 

 pour over them some water which has been boiled, so as to expel its air, meat im- 

 mersed in it will keep a long time, if the water be covered with a layer of oil, from 

 half an inch to an inch thick. Meat will also keep fresh for a considerable period 

 when surrounded with oil, or fat of any kind, so purified as not to turn rancid of itself 

 especially if the meat be previously boiled. This process is called ' potting.' 



Eggs. These ought to be taken new laid. The essential point towards their 

 preservation is the exclusion of the atmospheric oxygon, as their shells are porous, 

 and permit the external air to pass inwards, and to excite putrefaction in the albumen. 

 There is also some oxygen always in the air-cell of the eggs, which ought to be 

 expelled or rendered inoperative, which may be done by plunging them for 5 minutes 

 in water heated to 140 F. The eggs must then be taken out, wiped dry, besmeared 

 with some oil (not apt to turn rancid) or other unctuous matter, packed into a vessel 

 with their narrow ends uppermost, and covered with sawdust, fine sand, or powdered 

 charcoal. Eggs coated with gum arabic and packed in charcoal will keep fresh for 

 a year. Lime-water, or rather milk of lime, is an excellent vehicle for keeping eggs 

 in. Some persons coagulate the albumen partially, and also expel the air by boiling 

 the eggs for two minutes, and find the method successful. When eggs are intended 

 for hatching, they should be kept in a cool cellar. Eggs exposed, in the holes of 

 perforated shelves, to a constant current of air lose about ^ of a grain of their weight 

 daily, and become concentrated in the albuminous part, so as to be little liable to 

 putrefy. Each egg requires a hole in the shelf for itself. For long sea voyages, the 

 surest means of preserving eggs is to dry up the albumen and yolk by first triturating 

 them into a homogeneous paste, then evaporating this in an air-stove or a water-bath 

 heated to 125, and putting up the dried mass in vessels which maybe made air-tight. 

 When used, it should be dissolved in 3 parts of cold or tepid water. 



The excellent process for preserving all kinds of butchers' meat, fish, and poultry, 

 first contrived by M. Appert is described in the article MEATS, PRESERVED. That 

 article also contains a description of the methods now practised for the preservation 

 of Australian meat, which at the present time is largely imported into this country. 



PVTTV POWDER. Binoxide of tin, obtained by treating metallic tin with 

 nitric acid, when the metal is converted into hydrated metastannic acid, and this 

 when heated becomes anhydrous. In this state it is known as putty powder, and is 

 employed as a polishing agent ; it is also used to impart an opaque white colour to 

 enamels and dial-plates. 



PYRARGYRITE, or Dark-red Silver -ore. An antimonio-sulphide of silver, form- 

 ing a valuable ore at Andreasberg in the Hartz, in Mexico, and in Chile. See SILVER. 



PYRETHRU1VI. A genus of plants belonging to the natural order Composites. 

 It contains the feverfew and the pellitory of Spain. 



PYRIDINE, C'H 6 N (C'K 5 !^). A volatile base homologous with picoline, 

 lutidine, collidine, and parvoline. It was discovered by Anderson in bone-oil. It is 

 also contained in Dorset shale, naphtha, coal-naphtha, and in crude chinoline. 



PYRITES. A term originally applied to yellow sulphide of iron, because it 

 struck fire with steel. It is in strictness still confined to this mineral; but where 

 sulphur exists in combination with copper, cobalt, or nickel, these minerals also are 

 called pyrites. 



1. Iron Pyrites, Mundic ; Schwefelkies, Eisenkies. This important mineral is dimor- 

 phous, crystallising both in the cubic and rhombic systems, the latter variety being 

 known by the special name of Marcasite, or white iron pyrites. Its composition is a 

 bisulphide of iron, FeS 2 , containing 467 per cent, of iron and 53'3 percent, of sulphur ; 

 but on the large scale it almost invariably contains gold, from mere traces up to a 

 workable quantity (several ounces per ton), and by intimate association with copper 

 pyrites, copper ; such varieties are known as copper mundic, to distinguish them from 

 ordinary pyrites, or sulphur mundic, whose chief value is as a source of sulphuric 

 acid. 



Cubical pyrites octfurs in variously-modified crystals, the usual forms being cubes 

 or pentagonal dodecahedra, or combinations of both. The finest specimens are ob- 

 tained in the iron mines of Elba and Traversella : the colour is of a brassy-yellow, 

 with a nearly black streak, and the hardness (6 to. 7) about that of soft steel; sp. gr. 

 4-9 to 5-1. When heated alone, a portion of the sulphur is volatilised, leaving a mag- 

 netic sulphide ; but with the access of air the sulphur is burnt to sulphurous acid, and 

 may be completely expelled, the iron passing into the state of peroxide, which, if 



VOL. III. X X 



