794
SODA. —Sulphate of. Hargreaves’ Process.
of salt per twenty-four hours. This will only re-quire the attendance of one man at a time, againsttwo panmen and two or even four driers on theusual system. The consumption of coke is only ljcwt. per hour, or about one quarter of the fuel inordinary working; no breakages of pans are to beapprehended, and no skilled labour is required.The condensation of the hydrochloric acid is quiteas easy as in the old method, in spite of its dilutionwith the fire-gases, owing to its more steady andregular evolution. There is no more condensingspace than usual for a drier alone, and yet thestrength of the acid condensed is 30° Twaddle. Thissystem will probably be very extensively adopted byalkali makers. It will, however, have to be modi-fied in some details, as several alkali works usingit have met with important drawbacks to its use.Other mechanical furnaces are those invented byCammack and Walker, by Black and Hill, &c.
The sulphate of soda (called “ salt-cake ” in Lan-cashire and Ireland ), as drawn from the furnace,ought to show a bright yellow, lemon to orange,colour, which remains till it is quite cold. It ought tobe loose and of tolerably fine grain, with few lumps,or only quite friable ones. Undecomposed saltappears mostly in hard lumps, which break up withdifficulty, and show a honey-combed grey interior.When the sulphate shows a red colour (from ferricoxide), it is called “burned.” This hardly everoccurs, except in the case of weak sulphate. Somealkali makers like it in that state; the majority pre-fer it in the above-described state, and maintainthat “ burned” sulphate makes bad balls—probablybecause it is more difficult to decompose in the ballfurnace.
Testing of Sulphate of Soda for Commercial Purposes.—For the interior economy of alkali works, theonly points of importance are the “ free acid ”(really the hydro-sodic sulphate) and the undecom-posed sodium chloride. The former is usuallyexpressed in per cents, of SO g . The testing can bedone in a few minutes with sufficient accuracy for thatpurpose, by adding to a dissolved sample of sulphatestandard soda solution from a burette, till a changeof colour into brown and a slight precipitation offerric oxide show that all free acid has been neutra-lized. The sample is then tested with silver nitratefor chlorides, after adding some potassium chromate.For calcium and iron sulphate, 1J per cent, aregenerally assumed. This is, of course, not done formore accurate purposes, when the ordinary analyti-cal methods must be followed.
ANALYSES OF SULPHATE OF SODA (SALT-CAKE) BYG. E. DAVIS.
Insoluble in water,.
Dree sulphuric acid,.
Calcium sulphate,.
A.
B.
C.
0-112
0-955
1- 1390-682
2- 63294-393
0-987
0*073
1-820
1-148
0-588
0-234
96-137
0-042
0-022
1-046
0-322
0-744
97-824
100-000
100-000
100-000
A is from a “ blind roaster ” (muffle furnace) ; B,from an “open roaster” (reverberatory furnace);C, was made by Hargreaves’ patent process. Thefollowing are—
OLDER ANALYSES.
Chandelon.
Brown.
A
Sodium sulphate,.
Calcium sulphate,.
Magnesium sulphate.
Aluminium sulphate,.
Ferric sulphate,.
Lead sulphate,.
Sodium chloride,.
Sulphuric acid (S0 3 ),.
Moisture,.
Insoluble (sand),.
93-15
1-21
0-15
0-75
1-66
1-44
1-28
0-26
94-10
0-84
0-35
0-16
0-97
0-14
2-52
0-48
0-42
95-29
0-86
0-77
0-41
0-14
0*05
0-37
1-30
0-29
0-51
96-22
0-97
0*29
0-23
1*09
0-88
0-31
99-90
99-98
99-99
99-99
The following perfectly authentic calculation ofcost of sulphate of soda in 1874, from one of thelargest French chemical works, will present someinterest:—•
Francs.
Labour,.
Sulphuric acid,.
Grey salt,..
Nitre cake,.
Coal (6 cwts.),.
Articles in pottery,..
Sundries,.,..
Lighting,.
Residues....
Repairs of buildings,.
“ apparatus,..
General charges at works,.
“ “ Paris,. v
Pension fund (for men of thirtyyears’ employment,.
6*17
51*39
18-91
3*62
5*42
0-68
0-43
0-12
0*06
0-38
9-16
2*84
0-28
0-55
' 100*01 =
Deduct value of 1 £ ton hydrochloric \ o n . nn _
acid, at 32^ to 34J per cent., j
£4 0 014 0
Nett cost of salt-cake,
69-81 2 16 0
Each pan and furnace makes 2 tons per day.
Hargreaves' and Robinson's Process. —The sulphateof soda is produced by the direct action of sulphur-ous acid, oxygen (from air), and steam upon sodiumchloride. The gaseous products consist of hydro-chloric acid, together with nitrogen and excess ofsteam. The reaction commences at 750° Fahr., andincreases in intensity as the temperature rises. Whenthe supply of sulphurous acid is deficient, the hydro-chloric acid in the presence of oxygen is split upinto water and chlorine. The reaction occurringwhen the proper proportions are observed may berepresented as follows:—
S0 2 + O + 2NaCl + H 2 0 = Na 2 S0 4 + 2IIC1.
Salt, either in the form of rock or crystal, may beused; but the best results are obtained when finelydivided salt is moistened by exhaust steam, whichraises its temperature to 220° Fahr.; spread byrevolving arms on iron plates, and dried into hardflat cakes, and then cut into pieces about 1-J>- inchesdiameter. The iron plates travel slowly throughan oven like those used by biscuit bakers.