292 JOSEPH STRUTHERS 



slowly by dilute sulphuric acid, and on this account the sur- 

 face of zinc plates in galvanic batteries is usually amal- 

 mated. Tin amalgam is used to produce the reflecting surface 

 of ordinary mirrors, and amalgams of gold, copper, and 

 zinc are used in dentistry as fillings for teeth. 



In addition to the amalgams, mercury forms the fol- 

 lowing commercially important compounds: With chlorine, 

 mercurous chloride (HgCl), or calomel, largely used in med- 

 icine, and mercuric chloride (HgCy, or corrosive sublimate, 

 used in medicine and in surgery as an antiseptic, and also in 

 the preparation of anatomical specimens, and in the dressing 

 of furs and skins; with oxygen, mercurous oxide (HggO), 

 the suboxide or gray oxide of mercury which is of little im- 

 portance commercially, and mercuric oxide (HgO), the red 

 oxide of mercury or red precipitate, used in medicine and for 

 various other purposes in chemical analyses; with sulphur, 

 cinnabar, mercuric sulphide (HgS), or vermilion, the same 

 as cinnabar, the chief ore of mercury. 



Vermilion is invaluable as a pigment, because of the 

 permanence of its vivid cochineal red color. It is made 

 artificially in two ways — one, termed the dry method, in 

 which an intimate mixture of metallic mercury and sulphur 

 in proper proportions is heated in a retort and the sublimed 

 product condensed and ground very fine, the beauty of the 

 tint depending largely upon the fineness of the material; 

 and the other, called the wet method, by which various com- 

 pounds of mercury are transformed into the sulphide by the 

 use of chemical reagents. Vermilion prepared by the wet 

 method is of better quality than that made by the dry proc- 

 ess. The manufacture of vermilion has declined in recent 

 years on account of the competition of cheaper pigments 

 which have supplanted its use. The most important of 

 these is orange mineral (red lead), which is toned up to the 

 proper color by the use of eosin, one of the aniline dyes. These 

 imitation vermilions are now employed for almost all of 

 the more common uses, such as wagon painting, and while 

 they are inferior to the true mercury vermilion, from the 

 fact that they fade on exposure, yet they are a fairly satis- 

 factory substitute as long as they are protected by an ex- 



