A.
B.
c.
Insoluble matter.
23-000
1-948
4-664
Sodium hydrate,.
u carbonate,.
58-888
70-896
71-866
trace.
none.
0-722
“ chloride,.
6-135
14-040
10-729
“ sulphide,.
0-132
0-054
0-116
“ sulphite,.
0-151
0-063
0-074
*• sulphate,.
5-534
3-526
4-624
“ silicate.
0-683
trace.
trace.
kt aluminate,.
5-661
9’556
7-133
Total,.
100-184
100-083
99-928
The following is the composition of the insolublematter:—
A.
B.
Ferric oxide,...
Calcium oxide,.
Manganese oxide and magnesium \oxide,.j
2-146
93-000
4*332
0-522
1*179
94-006
4289
0-526
Davies.
Glendin-
Morison.
iiing, Tyne
A.
B.
Sodium hydrate,.
72-774
75-246
70-00
75-00
“ carbonate,...
1-419
2-536
6-00
1-50
chloride, ....
18-800
17-400
18-50
9-80
“ sulphate, ....
6-462
4-398
5-50
10-38
“ sulphite, ....
0-063
0-027
—
0-80
sulphide, ....
—
—
—
0-30
‘- silicate,.
0-304
0 297
—
0-44
u aluminate,...
trace.
trace.
__
0-31
Total,.
99-822
99-904
100-00
98-53
Davies.
Morison.
A.
B.
Sodium hydrate,.
83-840
89-600
82-00
“ carbonate,.
4-686
2-481
5-00
“ chloride,.
6-522
3-919
7-00
“ sulphate,.
4-526
3-419
6-00
“ sulphite,.
0-025
0-025
—
“ silicate,.
0-463
0-304
—
“ aluminate,. ..
trace.
trace.
—
Total,.
100-062
99-748
100 00
The caustic drums must be packed in three orfour instalments, otherwise a hollow core is left inthe centre, causing a loss in packing space. Glen-dinning and Edgar maintain that samples takenfrom different parts of a drum may show differentpercentages of alkali, but this is denied by Morison.
Caustic Soda from Red Liquors .—These (the motherliquors from the black-salt boat pans) generally standat 02° Tw.; the following is an analysis by Davies :—
Iron sulphide,. 0'313
Sodium bisulphide,. 0T95
“ sulphide, . 6 “256
“ sulphite,. IG‘022
“ hyposulphite,. 7'858
sulphate, . 14'848
“ chloride,. 65'526
silicate,. 9'677
11 aluminate,. 1'03I
“ carbonate, . 79"9GG
“ hydrate,. 194-400
“ sulphocyanide. 0'261
“ ferrocyanide,. 0'423
Grams, per litre,. 396'776
From these red liquors best white caustic issometimes obtained, but as a rule this is not done,and only the article called “cream caustic” is workedfor. Into its manufacture enter at the same timethe dissolved bottoms spoken of, and sometimestank liquor causticized in the usual manner. Thered liquor, thoroughly settled, is boiled down in aself-fired boat pan (say 30 feet X 8 feet X 2 feet 6inches), until it reaches 70° Tw., or a boiling pointof 250° Fahr. The pan is then cooled down andthoroughly fished. It is then re-heated to boiling,and 2-J to 3 cwts. nitre added; and when, after con-tinued boiling, a specific gravity of 94° Tw., or atemperature of 270° Fahr., is attained, a little morenitre is introduced (if requisite), and the whole afteran hour or two allowed to cool down. The clearliquor is run into a settler; the salts left behind arewashed with a little water to free them from nitre,and then removed and drained to be employed forthe manufacture of common “ caustic ash.” Thethoroughly settled liquor is run into a caustic pot.It appears then of a dark straw colour, and on boil-ing gives off ammonia copiously. In this case all thenitre ought to be added in the pans, and only verylittle, if any, should be put into the pots during thefinishing operation. The pot is fired carefully till asample tests 00 per cent, alkali, which is the usualstrength for cream caustic. It is not necessary to gofurther and bring the batch to igneous fusion, but itis baled out in that state, and without leaving anybottoms. Occasionally, however, the batch turnsred, and in this case nothing is left but to pack itand sell it for inferior caustic, or else to fire it toigneous fusion and make it into white caustic. Theoxidation by means of a current of air, instead ofthe nitre, is inadmissible for cream caustic, as thefinishing temperature is too low. The cream colouris due to the presence of ferric oxide, which is heldin suspension by the caustic soda at its comparativelylow finishing temperature, and which separates on dis-solving it in water. When cream caustic is preparedfrom uncausticized red liquor, as much as 1 cwt. ofnitre per ton of it is required; but the cost of evapora-tion is much less, and the time is saved altogether.
In the manufacture of caustic soda, water is anitem of considerable importance, as for every ton of70 per cent, caustic, 14^ tons of water have to beevaporated. In well-conducted works 100 tons of“salteake” (sulphate of soda) produce 54 to 57 tonsof 60 per cent, caustic soda, of which 9 to 11 percent, are “ bottoms.” The amount of salt necessaryfor reduction to 60 per cent, is generally 15 to 16per cent, of the caustic soda packed; that of nitre T)-to 2 per cent., of which about one-half is recoveredin the form of caustic alkali. The total quantity offuel used for all purposes should not exceed 6 to6J tons, divided as follows:—
Tons. Cwts.
Ball-furnaces, mixing-,. 1 0
“ firing,. 2 0
Boat pans,. 2 0
Caustic pots,. 1 0
Boilers,. 0 10
Total.. C> 10
_