210 



requisite, after dyeing with arnatto, to redden the silks with vinegar, alum, or lemon- 

 juice. The acid, by saturating the alkali employed for dissolving the arnatto, destroys 

 the shade of yellow that the alkali had given, and restores it to its natural colour, 

 which inclines a good deal to red. 



For the deep shades, the practice at Paris, as Macquer informs us, is to pass the 

 eilks through alum ; and if the colour bo not rod enough, they are passed through a 

 faint bath of Brazil wood. At Lyons, the dyers who use carthamus sometimes employ 

 old baths of arnatto for dipping the deep oranges. 



When the orange hues have been reddened by alum, they must bo washed at the 

 river ; but it is not necessary to beetle them, unless the colour turns out too red. 



Shades may bo obtained also by a single operation, which retain a reddish tint, em- 

 ploying for the arnatto bath a less proportion of alkali than has been pointed out. 



Guhliche recommends to avoid heat in the preparation of arnatto. He directs it to 

 be placed in a glass vessel, or in a glazed earthen one ; to cover it with a solution of 

 pure alkali ; to leave the mixture at rest for 24 hours ; to decant the liquor, filter it, 

 and add water repeatedly to the residuum, leaving the mixture each time at rest for 

 two or three days, till the water is no longer coloured ; to mix all these liquors, and 

 preserve the whole for use in a well-stopped vessel. 



He macerates the silk for 12 hours in a solution of alum, at the rate of an eighth of 

 this salt for one part of silk, or in a water rendered acidulous by the aceto-citric acid 

 above described, and he wrings it well on its coming out of this bath. 



Silk thus prepared is put into the arnatto bath quite cold. It is kept in agitation 

 there till it has taken the shade sought for ; or the liquor may be maintained at a heat 

 far below ebullition. On being taken out of the bath, the silk is to be washed and 

 dried in the shade. 



For lighter hues, a liquor less charged with colour is taken ; and a little of the 

 acid liquor which has served for the mordant may be added, or the dyed silk may be 

 passed through the acidulous water. 



We have seen the following preparation employed for cotton velvet : 1 part of 

 quicklime, 1 of potash, 2 of soda. 



Of these a ley is formed, in which one part of arnatto is dissolved ; and the mixture 

 is boiled for an hour and a half. This bath affords the liveliest and most brilliant 

 auroras. The buff (chamois) fugitive dye is also obtained with this solution. For 

 this purpose only a little is wanted ; but wo must never forget that the colours arising 

 from arnatto are all fugitive. 



Dr. John found in the pulp surrounding the unfermented fresh seeds, which are 

 about the size of little peas, 28 parts of colouring resinous matter, 26 '5 of vegetable 

 gluten, 20 of ligneous fibre, 20 of colouring extractive matter ; 4 formed of matters 

 analogous to vegetable gluten and extractive, and a trace of spicy and acid matters. 



The Gloucestershire cheese is coloured with arnatto, in the proportion of 1 cwt. 

 to an ounce of the dye : butter is sometimes coloured with it. 



When used in calico-printing, it is usually mixed with potash or ammonia and 

 starch. 



Arnatto was considered to contain two distinct colouring-matters, a yellow and red, 

 till it was shown by M. Preissor that one is the oxide of the other, and that they may 

 be obtained by adding a salt of lead to a solution of arnatto, which precipitates the 

 colouring-matter. The lead is separated by sulphuretted hydrogen ; and the sub- 

 stance being filtered and evaporated, the colouring-matter is deposited in small 

 crystals of a yellow-white colour. These crystals consist of bixine they become 

 yellow by exposure to the air, but if they are dissolved in water they undergo no 

 change. When ammonia is added to bixine, with free contact of air, there is formed 

 a fine deep red colour, like arnatto, and a new substance, called bixeine, is produced, 

 which does not crystallise, but may be obtained as a red powder ; this is coloured blue, 

 by sulphuric acid, and combines with alkalis ; it is bixine with addition of oxygen. 

 When arnatto, in the form of paste, is mixed from time to time with stale urine, it 

 appears probable that the improvement consists in the formation of bixeine from the 

 bixine by the ammonia of the urine. It has hence been suggested that, to improve 

 the colour of arnatto, it might be mixed with a little ammonia, and subsequently 

 exposed to the air, previously to its being used for dyeing. 



A solution of arnatto and potash in water is sold under the name of Scott's Nan- 

 keen Dye. 



Flag arnatto paid a duty of 18. 8d. per cwt., and the other sorts 51. 12s., previously 

 to 1832. The duty was subsequently reduced to Is. per cwt. on the former and 4s. 

 on the latter. It was repealed in 1845. 



AJINICA. A genus of plants belonging to the Natural order Composite, and Sub- 

 order Corymbifera. The Arnica montana, called Leopard's Bane, or Mountain 

 Tobacco, 18 a native of the North of Europe, and of the Alps. The plant contains a 



