Fig. 16. - Small gas cylinder made of gas-tube for adding alkyl chloride.

water, 1 gm.-molecule caustic soda lye, and 80 gms. soda. To this solution are added 500 c.cs. methyl (or ethyl) alcohol of 90 % strength, and it is then cooled to 10°. 1.75 Gm.-molecules methyl chloride or ethyl chloride are then added. The mixture is heated in an autoclave for 8 hours to 100° with stirring or rotation, at 4-5 atmos. The alkylation is then complete; the product is poured into water, the alkyl ether separated, and the spirit rectified. The alkyl derivative is washed with a little lye and water and should then contain no free nitrophenol. Working with ethyl or methyl chloride is no easy matter, for which reason the most convenient method is given here: the mixture of nitrophenol, soda and lye with aqueous alcohol is poured into the autoclave and the latter closed; it is not necessary to dissolve the substances. The autoclave is then evacuated by means of a water-pump and again closed by means of the valve. A small alkyl chloride bomb made from a piece of gas tube (1) 2 ins. in diameter with a screw nut (3) is then joined on to the autoclave by means of a copper tube (4), and a connection (2), (Fig. 16). The alkyl chloride should previously have been added to the bomb from a cooled glass cylinder, the bomb being placed in ice water for this purpose. As soon as the alkyl-chloride bomb has been attached to the autoclave (I), it is inverted (la) so as to permit the contents to run down the tube. It is now warmed by means of a very hot, wet cloth until one can only just touch it, after which the autoclave valve is opened (Fig. i6a). The warm alkyl-chloride immediately rushes into the evacuated autoclave, the valve of which is closed after a few seconds. It has been shown experimentally that by this means at least 98 % of the alkyl-chloride enters the apparatus. The bomb, which now has no internal pressure, may be removed and the autoclave warmed in an oil-bath as described above.

Fig. i6a. - Method of filling a laboratory autoclave with alkyl-chloride.

In the works alkylations are carried out in large horizontal or vertical boilers (see Chrysophenin). The alkyl-chlorides are always prepared from hydrochloric acid, alcohol, and zinc chloride. They are transported in large iron cylinders, and are stored in reservoirs. For use they are filled into steel bottles from which they are either pumped into the reaction vessel, or forced through an inlet tube by means of heat.

Trinitrophenol (Picric Acid).

Reaction:

Phenol.

Disulphonic acid.

Tnnitrophenol.

93 Gms. best quality phenol are placed in a glass,iron,or porcelain sulphonating pot. It is warmed to 100° with stirring, and 300 gms. monohydrate are then added, the temperature being kept below 110o, and maintained at 100-110o for a further hour to ensure the complete sulphonation of all the phenol. The greater portion of the phenol is converted into the disulphonic acid in this manner. By means of external cooling with ice and salt, the contents of the beaker are cooled down to o°, and to it are added drop-wise during 3 hours, 3.5 molecules nitric acid as 50 % mixed acid.

Commercial mixed acid is made from very concentrated nitric acid and highly concentrated oleum. Usually nitric acid of sp. gr. 1.48 is mixed with 40 % oleum in large, water-cooled iron kettles. In the laboratory this process is not carried out owing to the great danger. It suffices on the small scale to mix nitric acid of sp. gr. 1.50-1.52 with its own weight of monohydrate.

As soon as all the nitric acid has been dropped into the phenol-sulphonic acid, the mixture is allowed to stand over-night at the ordinary temperature, and next day it is warmed very slowly with stirring on the water-bath to 300 during 1 hour. The temperature is then raised to 45°, but no higher, otherwise the mass may suddenly heat up of its own accord; in this case, even if there is no explosion, all the contents will be forced out of the kettle. The reaction,

93 gms. Phenol. 300 Ccs. H2So4 (100 %).

440 gms.

50 % mixed acid.

Fig. 20. - General arrangement of a colour

1. Hydraulic press.

2. Filter-press with wooden trays for the filter-cake.

3. Pressure vat with iron supports.

4 and 5. Wooden vats with mechanical stirring gear.

Plate VII.

used in the dye industry (scale 1:100).

6. Ventilating shaft with steam jet.

7. Driving shaft and wheel.

8. Pressure pipe from autoclave.

9. Travelling crane (10 tons).

1o. Autoclave. Capacity 1 1/2 cubic metres. 1 and 12. Hoists (3 tons).

however, cannot be completed at 45°. A small portion, therefore, of the nitrating mixture (about 50 c.cs.) is placed in a porcelain dish of 1 1/2 litres capacity and warmed, with stirring, on the sand-bath. The temperature rises rapidly to 110-125o, after which the rest of the mixture is dropped slowly with continuous stirring on to the pre-heated portion, so that no frothing over can take place. The heating is continued for a further half-hour at 110-120o, after which sufficient water is added to produce a sulphuric acid of about 40 %, keeping the temperature at 120o. For this purpose about 700 c.cs. of water are required, as may be easily calculated. Nitrous fumes are evolved, but only in small quantities if the nitration has been properly carried out. The picric acid separates quantitatively on cooling as it is insoluble in 40 % sulphuric acid. A certain amount of resinous and other decomposition products remain in the mother-liquor. The picric acid is filtered, after cooling, through a cotton filter, and is washed with cold water, after which it is chemically pure. A yield of about 210 gms. pure product is obtained.

In the same way are prepared Martius Yellow (dinitronaphthol 1:2:4), Naphthol Yellow S (dinitronaphthol monosulphonic acid 1:2:4:6), as also dinitro-cresol and other polynitro compounds. With a sufficient concentration of the nitrating mixture, practically the theoretical quantity of nitric acid will suffice.

Notes on Works Technique and Practice. - All the liquids mentioned are strongly acid, and must therefore be filtered through acid-proof material: e.g. stone suction filters (Fig. 14, Plate V.), or gun-cotton filter-cloths (nitro-filters). The nitrous gases evolved during the nitration are condensed to nitric acid in towers provided with Raschig-rings.

700 c.cs. Water