2.5.21

Eosine a Substitute for Litmus.

Practical Magazine 13, 1876

(Chemistry applied to the Arts, Manufactures, &c. Dyeing, Calico Printing, Bleaching, Tanning, and Allied Subjects.)

MEISTER recommends the brilliant new dye, eosine (see “Practical Magazine,” August, 1875), as a substitute for litmus in testing for alkali. Eosine changes instantaneously when exposed to the slightest alkaline action, whereas the change of colour in litmus is progressive.

- Moniteur Indust. Belge, 1st Mov. 1875.

Sand’s Leather-Blacking.

Practical Magazine 13, 1876

(Chemistry applied to the Arts, Manufactures, &c. Dyeing, Calico Printing, Bleaching, Tanning, and Allied Subjects.)

This well-known useful blacking for leather may be made thus: Dissolve 22 lbs. of green vitriol and 5 lbs. of tartaric acid in 9 gallons of water. After the settling, draw off the clear liquid ; then boil 16 lbs. of logwood with about 18 gallons of water and 11 gallons of the fluid. Let the boiled mixture stand for about eight days, pour it off from the sediment, dissolve in it 2 lbs. of grape sugar, and mix this liquid with the green vitriol solution. The blacking so obtained may be made still brighter by mixing the logwood decoction with 4 lbs. of aniline black-blue before the addition of the vitriol. The application of the blacking is very simple. The leather is first well brushed with a solution of soda, or still better with spirit of sal-ammoniac, in twenty-five times as much water, to get rid of the grease. The blacking is then applied with the proper brush for the purpose.

- Stummer's Ingenieur, Dec. 17, 1875.

Chromate of Iron.

Practical Magazine 13, 1876

(Chemistry applied to the Arts, Manufactures, &c. Dyeing, Calico Printing, Bleaching, Tanning, and Allied Subjects.)

If to a solution of neutral chromate of lead be added a solution of chloride of iron sharpened with hydrochloric acid, a dusty precipitate is formed of a bright orange colour. This is chromate of iron, which, dried at 104° Fah., is found to be composed of 65 to 65.11 per cent. of chromic acid and 34.58 to 34.71 of oxide of iron, a composition represented by the formula (Cn. O4)3 Fe2, and corresponding mathematically to 65.33 of chromic acid with 34.66 of oxide of iron.

This chromate of iron is insoluble in water, easily soluble in hydrochloric, nitric, and sulphuric acids, and decomposes when it is digested in a ley of soda. When strongly heated, it swells and changes to a blackish brown.

Chromate of iron may be conveniently used for oil-painting, for, though in vivacity of colour, it is not equal, to chromate of lead, it has the advantage over it of not blackening under the action of hydro-sulphuric acid, and being in all circumstances without injurious effect on the health. Lastly, chromate of iron may be obtained at a much lower price than chromate of lead.

- Technologiste