39
Class 31.] SALTS OF SEA-WATER—BICHROMATE AND PRUSSIATES OF POTASH.
present manufactured in this way. The acid thus pre-pared, is of course free from lead. The manufacture ofvessels of the material described, for chemical purposes,being greatly on the increase in England, the process ofJaveL could be easily introduced, and appears well de-serving of the consideration of manufacturers.
Salts of Ska-Water. 1
A Council Medal was accorded to MM. Prat and jAoahd, of Marseilles (1082, p. 1257), for various salts, in- :eluding the chloride of potassium, sulphate of soda, and ,sulphate of magnesia, prepared from sea-water, by the pro-cess of M. Bulard. The long-continued investigations of ;sea-water, by the last-named eminent chemist, have fur-nished valuable means for the separation of its useful salts.
It appears that the sea-water of the Mediterranean maybe concentrated by spontaneous evaporation to density1*27, without depositing anything but common salt. The :mother-liquor, or bittern, when further concentrated, :first deposits, as its density rises from 1*27 to 1*32, amixed salt, consisting of about 40 parts of sulphate ofmagnesia and GO parts of chloride of sodium. Or, if .the temperature falls to G" or 7 Centigrade (43" or 45° !Fahr.), bittern of density 1*32 deposits sulphate of mag-nesia nearly pure, in the proportion of about 90 kilo- \grammes of that salt from one cubic metre of fluid.The most economical application of this sulphate of .magnesia is said to be in the conversion of chloride of ,sodium into sulphate of soda. The next importantproduct obtained is, the double chloride of potassiumand magnesium, which serves afterwards for preparingthe chloride of potassium. This double salt is depositedfrom the bittern concentrated to density 1*345, by spon-taneous evaporation, after the deposition of the magnesiansalts: or by concentrating by artificial heat in an eva-porating pan to the same extent. Dissolved in a smallquantity of hot water, the double chloride undergoesdecomposition, and allows the chloride of potassium tocrystallize nearly pure on cooling. The last mother-liquor above density 1*345, after the separation of thepotash, contains much chloride of magnesium; a saltwhich may be had recourse to as a source of hydro- :chloric acid, being decomposed by distillation.
M. Balard has also proved that the greater portion of .the sulphate in sea-water, separates, as sulphate of soda,from sea-water concentrated to from density 1*152 to1 2, if cooled down to from —4 to —5 Centig. (25C to23 Fahr.). Waters concentrated as far as density 1*2 to1*2G4, produce an abundant deposit of sulphate of soda,even at —2' or—3 Ceutig. (2S to 26° Fahr.). Sulphateof soda, however, is procured more conveniently by dis-solving together sulphate of magnesia and chloride ofsodium, in the proportion of 55 of the former to 45 of thelatter, at the temperature of 30° Centig. (80° Fahr.), andrunning off the solution of density 1*2G4 into open reser-voirs. Such a solution exposed during a cold night inwinter, deposits a considerable quantity of sulphate ofsoda at 5 r or G 3 Centig. (42° Fahr.); about 85 per cent,of the whole quantity of that salt which it contains,at 4* - 11 Centig. (35‘G 3 Fahr.) ; and if the temperaturefall to —2° (28*4° Fahr.), the solution deposits nearlythe whole of the sulphate of soda present.
The most important of these products is, no doubt, thechloride of potassium, and M. Balard has, with goodreason, looked to sea-water as the great natural source ofpotash. The water of the Mediterranean contains, ac-cording to the analysis of M. Usiglio, 0*0505 pound ofchloride of potassium in 100 pounds of water, or about onetwo-thousandth part of its weight of that salt.
The bichromate of potash was exhibited to great advan-tage by Messrs. Dentith (8, p. 187), and other makers.Prior to 1820, the process universally followed for the pre-paration of this salt was, to calcine chrome iron with ni-trate of potash. Bichromate of potash appears to have beenconsumed, at that time, in the preparation of chromate oflead only, and was sold at about 2Is. per lb. The firstalteration in the process was the addition of carbonate ofpotash to the chrome ore and nitre, by which a saving of
the latter salt was effected. The next great improvementmade in the manufacture was the dispensing with nitre,and oxidising entirely by means of air admitted into thereverberatory furnace in which the ore mixed with car-bonate of potash is calcined. This change took placeabout 1835 or 183G. An addition of lime to the precedingmaterials was made by Stromeyer, in Norway , a few yearsafterwards, and soon became general. 'The oxidation goeson quicker with the presence of lime, owing to the porosityof the mass, which allows the more ready access of air.The earliest great manufacturers of this salt in the UnitedKingdom were Kurtz and Niven, of Manchester, andTurnbull and Ramsay, of Glasgow , who were soonfollowed by the Whites in Glasgow , Swindells in New-castle, and Dentith in Manchester.
The introduction of the yellow discharge (chromate oflead) upon Turkey-red cloth, by Daniel Koechlin, ofMulhouse , about 1820, appears to he the circumstancewhich first greatly increased the demand for this salt,and stimulated the improvement of its manufacture.Besides its familiar application, to produce the yellowand orange chromates of lead, bichromate of potash isnow used in dyeing wool; a fast and solid black beingproduced by boiling the wool with bichromate and alittle sulphuric acid, washing the wool in water, andafterwards dyeing with logwood in the usual way. Bysubstituting other dye-stutfs for the logwood, variousother colours are produced in a similar manner. Thewool contains oxide of chromium, which acts like alu-mina or peroxide of iron in attaching colouring matters.Chromic acid has also been used in bleaching palm oil,and in oxidising oils for other purposes.
The following statement (kindly supplied to me byMr. J. White, of Shawfield, Glasgow ) of the entireproduction, during several quinqueunial periods, of oneof the oldest and most considerable manufactories ofbichromate of potash in Scotland , gives a fair idea, Ibelieve, of the general advance of this manufacture, during the period alluded to :—
Ver Pound.
In five vears— s. d.
1825-
-1830, 315 tons bichromate
of potash,
at
2
0
1830-
-1835, 1256 tons .,
5 ?
at
1
0
1835-
-1840, 1870 tons ,,
at
0
9
1840-
-1845, 2840 tons ,,
at
0
8
1845-
-1850, 2670 tons ,,
?>
at
0
-i
1 1
These important salts were exhibited of great purityand beauty, by several manufacturers, particularlyMessrs. T. Bramwell and Co., of Newcastle (27, p. 190;;the l-Icu let and Campsie Alum Company, of Glasgow (13, pp. 188, 189); the Bocxwillkr Mining Company,of France (37G, p. 1195); C. Schlippe, of Russia (27, p.13G7), and Alexander Brusgiiin (24, p. 1367), also ofRussia .
The manufactory of Messrs. Bramwell was establishedabout 80 years ago, at which time Prussian blue onlywas made in it; a considerable quantity of which, 1 aminformed by Mr. Bramwell, was sent annually to China ,and used by the Chinese, it was believed, for colouringgreen teas: a spring shipment was always made ofabout 2,000/. in value, which was often followed byanother in autumn. It was first sold at two guineasper pound, made up in neatly-finished one-pcimdpackages, hut had fallen, in 1815, to 10s. Cd., and about1820 to 2s. Cid, For the last ten years the price ofPrussian blue has been Is. 9c/.
Prussiate of potash was not known in commerce iu acrystallized state till about 1825, when the price was5.w per pound. But for some years previously a weaksolution of the salt, or of the fiuxed mass of animalmatter and potash, had been sold at Is. per gallon. Theprocess of manufacture, so far as regards the materials usedand the furnaces employed, is still essentially the same asit was fifty years ago; but in consequence of agitating thefluxed mass by machinery in closed pots, introduced atGlasgow by the late Charles Macintosh , in 1824, andether minor improvements in the manipulation, theproduction of pnusiate from the same quantity of