FRENCH PURPLE 489 



Tho continuous apparatus is more complicated in construction ; it consists of a 

 boiler or distilling vessel, with the addition of a rectifier, formed of a series of 

 horizontal tubes in which the gas is freed from the last trace of water by a current 

 of weak ammonia water circulating in the opposite direction. From the rectifier the 

 gas passes to a serpentine tube, forming part of the boiler, and thence into the con- 

 denser, a series of tubes cooled by a current of water to 60 Fahr. Here the gas is 

 liquefied, and is driven over by the pressure in the boiler into a regulator, from which 

 it passes into the freezing vessel, also formed of a series of spiral tubes, which are 

 surrounded by a solution of chloride of calcium ; the moulds containing the water to 

 be frozen are placed in a vibrating frame, in order to cause the ice to form more 

 rapidly. The return current of ammoniacal gas from the freezing vessel is passed 

 over by an exhausting pump into a receiver, where it is redissolved in the spent water 

 drawn from the boiler. Tho ice produced in the continuous apparatus varies between 

 eight and fifteen times the weight of the fuel consumed : about a gallon of condensing 

 water is required for every pound of ice produced. For some further matters connected 

 with this peculiar condition, see WATER. 



FREXBERGXTE. An argentiferous fahlerz. See FAKLERZ. 



FREIESX.EBENXTE. A sulphide of silver, lead, and antimony. See SILVER. 



FRENCH BERRIES. The berries of the Ehamnus catharticiis, and other species 

 of the Buckthorn. The true French berries, which should be four-seeded, belong to 

 the first named ; all the two-seeded berries are obtained from other and inferior kinds. 

 See BUCKTHORN. 



FRENCH CHAZiK. A steatite ; a soft magnesian mineral. 



FRENCH POLISH. There are numerous methods given for the preparation of 

 this polish ; one of the best is probably the following: 1 Ib. of shell lac dissolved in 

 a gallon of spirits of wine without heat. Another recipe is 12 ounces of shell lac, 

 2 ounces of gum elemi, and 3 ounces of copal to 1 gallon of spirits of wine. 



FRENCH PURPZiE. Amongst the most important of the modern improvements in 

 the preparation of colouring matter from the lichens may bo mentioned the preliminary 

 extraction of the colouring acids of the lichens by digestion with an alkali (potash or 

 lime) and the subsequent precipitation of these acids, whereby they are completely 

 separated from the woody matters and other impurities. Dr. Stenhouse, to whom 

 tliis valuable suggestion is due, recommends manufacturers to macerate the lichens 

 on the spot with milk of lime, and then to precipitate the clear solution by means of 

 an acid such as hydrochloric, or acetic acid, whereby the colour-yielding acids are 

 separated. By subjecting these acids, more or less pure, to the action of air and 

 ammonia, products are obtained not only free from woody fibre, but exhibiting 

 brighter and deeper colours, not to speak of the economy and facility of manipu- 

 lating a much smaller bulk of material during the most important stage of the manu- 

 facture. 



Archil prepared by the usual methods, notwithstanding its fine colour, has the 

 defect of being extremely liable to change by the action of acids and alkalis, and of 

 easily deteriorating in colour when applied to silk, wool, or animalized cotton. 

 Eecently, however, a new kind of archil has been prepared, under the name of 

 French Purple, distinguished in the first place by its very pure mauve or dahlia 

 colour, and, secondly, by being much faster than common archil, and less sensitive to 

 the action of acids. 



This beautiful colour has been introduced and is chiefly manufactured by MM. 

 Guinon, Marnas, and Bonnet, of Lyons. It is prepared as follows : The lecanoric, 

 erythic, evernic acids, &c., of the lichens are extracted by digestion with ammonia ; 

 the mass is pressed, the solution precipitated by a mineral acid, and the precipitate 

 collected, washed, and re-dissolved in ammonia by the aid of heat, whereby a solution 

 is obtained which, on exposure to the air at a temperature of 19 or 20 C., 

 gradually assumes a very bright red colour. As soon as the tint has acquired 

 sufficient intensity the liquid is introduced into shallow basins, and very slowly 

 evaporated at a temperature between 40 and 60 C., care being taken not to exceed 

 the latter limit. By this evaporation in contact with the air the liquid after a few 

 days acquires a very deep violet colour, which undergoes no further change even 

 by the action of acids. The violet solution, super-saturated with a strong acid, 

 yields a copious flocculent precipitate of a very fine and rich garnet colour, which 

 when collected on a filter, and washed to remove the saline mother liquid, constitutes 

 French purple. 



The dye thus prepared has not, however, attained the highest degree of beauty and 

 purity of which it is susceptible. When used directly for dyeing wool or silk (for 

 which purpose it does not require the aid of mordants, the colouring matter being 

 simply dissolved in ammonia, and the solution diluted with the proper quantity of 

 water), it imparts to them a violet colour having a reddish cast. 



