CALOMEL 673 



KEMP. A fibre obtained from one of the Asiatic nettles probably 

 tho Urtica tenacissima, which, is a native of Sumatra and Kungpore. Its fibres are 

 exceedingly strong, and are converted into cordage. China-grass cloth, and some 

 other fabrics are made from the fibres of the Nettle. See NETTLE. 



CAXiXiOW. The top or rubble bed of a quarry. This is obliged to be removed 

 before the useful material is raised ; it is the great source of expense in working a 

 quarry. (Brande). Frequently termed the ' overburthen.' 



CAIiLYS or KAXiIiTS. An old Cornish term, still used in the remote mining 

 districts, and applied to hard ground chiefly to a variety of the Killas or Clay 

 Slate. 



CAXiOMEIi. (Chlorure de Mercure, Fr. ; Kalomd, Chlormercur, Versiisstes 

 Quecksilbcr, Ger.) The sub-chloride of mercury, or mercurous chloride of modern 

 chemists, Hg 2 Cl (Kgr 2 Cl 2 ). Calomel is found native in the Palatinate, in crystals 

 often well defined, coating the cavities of a ferruginous gangue, associated with cin- 

 nabar ; also at the quicksilver mines of Idria in Carniola, at Almaden in Spain, and 

 Horzowitz in Bohemia. The native calomel is known as horn-quicksilver. The manu- 

 facture of this substance upon the large scale may be performed in various ways. 

 Tho cheapest, and most direct consists in mixing ll part of pure quicksilver with 1 

 part of pure nitric acid, of specific gravity from 1*2 to 1'25; and in digesting the 

 mixture till no more metal can be dissolved, or till the liquid has assumed a yellow 

 colour. At the same time, a solution is made of 1 part of common salt in 32 parts of 

 distilled water, to which a little muriatic acid is added ; and when heated to nearly tho 

 boiling point, it is mixed with the mercurial solution. The two salts exchange bases, 

 and a subchloride of mercury precipitates in a white powder; which, after being 

 digested for some time in the acidulous supernatant liquor, is to be washed, with the 

 greatest care, in boiling water. The circumstances which may injure the process are 

 the following : 1. When less mercury is employed than the acid can dissolve, there 

 is formed a nitrate of mercury which gives rise to some corrosive sublimate and 

 causes a proportional defalcation of calomel. 2. If the liquors are perfectly neutral 

 at tho moment of mixing them, some sub-nitrate of mercury is thrown down, 

 which cannot be removed by washing, and which gives a noxious contamination 

 to tho bland calomel. The acid prescribed in the above formula obviates this 

 danger. 



The following are the directions given by the London College for the preparation 

 of this salt : 2 Ibs. of mercury are boiled to dryness in a suitable vessel with 3 Ibs. of 

 concentrated sulphuric acid : the sulphate of mercury thus obtained is rubbed when 

 cold, first with 2 Ibs. more mercury in an earthen vessel until perfectly mixed, and 

 then thoroughly incorporated with 1 Ib. of chloride of sodium ; the whole is then 

 sublimed in an appropriate vessel ; the sublimate is rubbed to a fine powder, and 

 then washed with boiling distilled water, until the washings are no longer tinged 

 by sulphuretted hydrogen. This process is absolutely necessary in order to re- 

 move every trace of corrosive sublimate which is always formed in greater or less 

 quantity. 



At Apothecaries' Hall 50 Ibs. of mercury are boiled with 70 Ibs. of sulphuric acid 

 to dryness in a cast-iron vessel ; 62 Ibs. of the dry salt are triturated with 40 J Ibs. of 

 mercury until the globules disappear ; and 34 Ibs. of common salt are then added. 

 The mixture is submitted to heat, and from 95 Ibs. to 100 Ibs. of sublimed calomel are 

 obtained. It is washed in large quantities of distilled water, after having been ground 

 to a fine and impalpable powder. 



According to the patent of Mr. Josiah Jewell, the vapour of calomel was to be 

 transmitted into a vessel containing water, in order to condense it at once into an 

 impalpable powder. But this process was beset with many difficulties. The vapour 

 of the calomel was afterwards introduced into a large receiver, into which steam was 

 simultaneously admitted ; but this plan has also been found to be precarious in the 

 execution. The best way is to sublime the calomel into a very large chamber from 

 an iron pot, in the same way as the flowers of sulphur are formed. The great body 

 of cool air serves to cause the precipitation of the calomel in a finely comminuted 

 state. It is afterwards washed with water, till this is no longer coloured by sulphu- 

 retted' hydrogen. 



A patent was obtained in September 1841, by Anthony Todd Thomson, M.D., for 

 an improved method of manufacturing calomel and corrosive sublimate, as follows : 

 This invention consists in combining chlorine in the state of gas with the vapour of 

 mercury or quicksilver, in order to produce calomel and corrosive sublimate. The 

 apparatus employed consists of a glass, earthenware, or other suitable vessel, mounted 

 in brickwork, and communicating at one end with a large air-tight chamber, and at 

 tho other end by means of a bent tube, with an alembic, such as is generally used in 

 generating chlorine gas. The alembic is charged with a mixture of common salt, bin- 



Vot.1, 



