PEARLS 517 



the long-continued action of carbonic acid on tho metal buried in the soil. It is very 

 commonly imitated by fraudulent dealers. Patina, or Patella, was also the name of 

 a bowl made of either metal or earthenware. Fairholt. 



PAUXi VERONESE GREEN. An artist's colour; a peculiarly-prepared 

 carbonate of copper. 



PEACH. A Cornish, miner's term, given to chlorite and chloritic rocks. A 

 peachy lode is a mineral vein containing this substance, generally of a bluish-green 

 colour, and rather soft. See CHLORITE. 



PEACH-WOOD, or Nicaragua, and sometimes termed Saint Martha Wood, ia 

 inferior to the other two named ; but is much used in the dyehouse, and, for many 

 shades of red, is preferred, although the colouring-matter is not so great. It gives a 

 bright dye. The means of testing the quality of these woods by the dyer is similar to 

 that described for logwood, with the same recommendations and precautions. Napier 

 on Dyeing. 



PEACOCK-COPPER ORE. An iridescent copper pyrites, produced by a 

 partial decomposition of tho yellow ore. The boys and girls employed in the mines 

 produce this condition artificially by putting the ordinary copper pyrites into warm 

 water holding sulphate of copper in solution ; and sell the beautifully-coloured spe- 

 cimens to strangers. A more effective way of producing this peacock copper is to 

 take a lump of yellow copper-ore (copper pyrites), and, having bound a piece of 

 copper wire around it, to connect the other end of the wire with a plate of copper. 

 If this arrangement be made in a vessel divided by a porous partition, having a 

 solution of sulphate of copper on the side in which the copper ore is placed, and salt 

 and water on the other side, the change goes on rapidly, and the result is exceedingly 

 permanent. 



PEARZiASH. Commercial carbonate of potash. See POTASH. 



PEARK BARXiEY. See BARLEY. 



>EARXiS (Perles, Fr. ; Pcrlen, Ger.) are the productions of certain shellfish, such 

 as the pearl-oyster. These mollusca are subject to a kind of disease caused by the in- 

 troduction of foreign bodies within their shells. In this case their pearly secretion, 

 instead of being spread in layers upon the inside of their habitation, is accumulated 

 round these particles in concentric layers. Pearl consists of carbonate of lime, inter- 

 stratified with animal membrane. 



The oysters whoso shells are richest in mother-of-pearl are most productive of 

 these highly-prized spherical concretions. The most valuable pearl-fisheries are on 

 the coast of Ceylon, and at Olmutz in the Persian Gulf ; and their finest specimens 

 are more highly prized in tho East than diamonds, but in Europe they are liable to 

 be rated very differently, according to the caprice of fashion. When the pearls are 

 large, truly spherical, reflecting and decomposing the light with vivacity, they are 

 much admired. But one of the causes which renders their value fluctuating, is the 

 occasional loss of their peculiar lustre, without our being able to assign a satisfactory 

 reason for it. 



The following letter on the Ceylon pearl-fishery, recently written by E. W. H. 

 Hoklsworth, is of interest : 



' Skates are no new enemy to the pearl-oyster. It is an old idea among the divers 

 that tho several failures of the fishery have been due to the depredations of these 

 fishes, and the subject was one of those to which my attention was specially directed 

 when I was sent out by the Government in 1865 to enquire into the causes of the 

 failure in the previous year. Skates naturally feed on shell-fish, and they are pro- 

 vided with teeth which enable them easily to crush the pearl-oyster, many of the 

 broken pieces of shell being rejected, while other parts are swallowed with the oyster 

 itself. But skates have no means of extracting the fish and leaving the shells unin- 

 jured. In 1864, when the Ceylon Government expected to obtain from the pearl- 

 banks a revenue of 50,000^., the principal bed was found covered with empty shells, a 

 large portion of them with the valves united at the hinge, and otherwise uninjured. 

 This was precisely the appearance which the oysters would have presented had they 

 died a natural death, as I pointed out in my official reports. There were a few living 

 oysters, and, in addition, a considerable number of broken shells. These last were 

 doubtless the work of the skates. 



Pearl-oysters attain their full superficial growth in about four years, but the shell 

 thickens for two years more, and it is during this period the pearls rapidly increase 

 in size. After about six years, the animal dies, the shell opens, and the contents 

 disappear. It is, of course, desirable to leave tho oysters on the banks as long as 

 possible in order to obtain large pearls, but there is the danger of leaving them too 

 long and losing them altogether. That is what occurred in 1864. I obtained ample 

 evidence to satisfy mo that the oysters should have been fished in 1863, for, according 

 to official reports, they were beginning to die off in February of that year, and then 



