1090 WAFERS 



and separated by filtration from the residue of arseniate of iron. The green liquid, 

 which now contains more or less cobalt, iron, nickel, and manganese, is mixed with a 

 filtered solution of pearlash, until the dirty red precipitate begins to turn blue. 

 Care and experience in this operation are requisite, otherwise a loss of cobalt might 

 result. The precipitate of arseniate and carbonate of iron, which at the same time 

 contains nickel and manganese, is separated by filtration, and the beautiful red 

 liquid mixed with more of the solution of pearlash until the whole of the cobalt is pre- 

 cipitated ; the precipitate is carefully washed and dried. This hydrated oxide of cobalt 

 is sufficiently pure for technical purposes, and answers just as well as that prepared 

 from oxalate of cobalt or by caustic ammonia. 



For painting, the oxide of cobalt is heated in a Hessian crucible with 1 part silica, 

 and 1 J part oxide of zinc for two hours in a blast-furnace, then reduced to a fine 

 powder in a porcelain mortar, and mixed with an equal weight of lead-glass. 



Yellow Colour. A beautiful yellow is obtained from 2 oz. minium, ^ oz. Slib. oxydat. 

 alb. abl. 2 drms. oxide of zinc, 2 drms. 2 scruples calcined borax, oz. silica, -J drm. 

 dry carbonate of soda, and 1 scrupled/err, oxydat. fuscum, which are well mixed, fused 

 in a crucible, and then ground fine. Wae'chter. ' 



VITRIOL, from Vitrum, ' glass,' is the'old chemical, and still the vulgar appellation 

 of sulphuric acid, and of many of its compounds, which in certain states have a glassy 

 appearance : thus : Vitriolic acid, or oil of vitriol, is sulphuric acid ; blue vitriol, is 

 sulphate of copper; green vitriol, is green sulphate of iron; vitriol of Mars, is red 

 sulphate of iron ; and white vitriol, is sulphate of zinc. 



VIVIANITE. A blue iron ore, phosphate of iron. Some fine examples have 

 been found in the mines of Cornwall and Devon. See IRON ORES. 



VOLCANIC CLASS. See OBSIDIAN. 



VORTEX WATER-WHEEL. See TURBINE. 



VRXAC. A name given to kelp by the French makers ; vriac venant, drift weed ; 

 vriac scie, cut weed. The same as VAREC, 



VULCANITE. Vulcanised india-rubber. See CAOUTCHOUC. 



VULPINITE. A siliceous variety of anhydrite; containing 8 per cent, of silica. 

 The vulpinito from Vulpino, near Bergamo in Italy, takes a fine polish, and is used 

 for ornamental purposes. It is known to artists as the Marmo Bardialio di Bergamo. 



w 



WACXE is an obsolete name for a rock intermediate between clay-slate and 

 basalt. It is generally an earthy decomposing igneous rock. 



WAD, or WADD. is the provincial name of plumbago in Cumberland ; and also 

 of an ore of manganese in Derbyshire and elsewhere, which consists of the peroxide 

 of that metal, associated with nearly its own weight of oxide of iron, &c. 



WADDING- (Ouate, Fr. ; Watte, Ger.) is the spongy web which serves to Hue 

 ladies' dresses, &c. Ouate, or Wat, was the name originally given to the glossy 

 down tufts found in the pods of the plant commonly called Apocyn, and by botanists 

 Asdepas Syriaca, which was imported from Egypt and Asia Minor for the purpose of 

 stuffing cushions, &c. Wadding is now made with a lap or fleece of cotton prepared 

 by the carding-engine (see Carding, COTTON MANUFACTURE), which is applied to 

 tissue-paper by a coat of size, made by boiling the cuttings of hare-skins, and adding 

 a little alum to the gelatinous solution. When two laps are glued with their faces 

 together, they form the most downy kind of wadding. 



WAFERS. There are two manners of manufacturing wafers : 1, with wheat- 

 flour and water, for the ordinary kind ; and 2, with gelatine. 1. A certain quantity 

 of fine flour is to be diffused through pure water, and so mixed as to leave no glotty 

 particles. This thin pap is then coloured with one or other of the matters to bo par- 

 ticularly described under the second head; and which are, vermilion, sulphate of 

 indigo, and gamboge. The pap is not allowed to ferment, but must be employed 

 immediately after it is mixed. Wafers are now but little used, adhesive envelopes 

 having almost superseded them. 



The colouring-matters ought not to be of an insalubrious kind. 



For rod wafers, carmine is well adapted, when they are not to be transparent ; but 

 this colour is dear, and can be used only for the finer kinds. Instead of it a decoction 

 of brazil-wood, brightened with a little alum, mny bo employed. 



For yellow, an infusion of saffron or turmeric has been prescribed ; but a decoction 

 of weld, fustic, or Persian berries, might be used. 



