932 SULPHURIC ACID.— Uordhausen Acid.

moisture from the air, on which account it is neces-sary to use glass retorts or platinum stills in theplace of open pans, to bring the acid to its higheststrength. Pour parts of acid and 1 of ice produceheat, but 4 parts of snow and 1 of acid producecold (Brande).

Oil of Vitriol from Copperas. — Ordinary strongsulphuric acid of about 150° Tw. (specific gravityT750), easily freezes when standing in a carboy atabout 40° Fahr. or under, and is difficult to liquefyagain.

Sulphuric acid displaces the greater part of theother acids from their combinations, and at ordi-nary temperatures decomposes phosphates andborates; but at a red heat the phosphoric andboracic acids expel sulphuric and its bases. In con-sequence of its strong affinity for water it charsmost organic matters, and it acquires a brown tingefrom the smallest particles of straw or dust, &c.It dissolves small quantities of charcoal, as well assulphur, tellurium, and selenium; and these bodiesgive it various shades of brown, red, and green, orblue. In consequence of its extensive use in manu-factures, it is important to the consumer to have aready method of ascertaining its strength. Severalvaluable tables have been drawn up by Dalhou,Parkes, and Dr. Uris, to show its strength andcommercial value; the table by Dr. Ure is generallyreferred to as the standard. Glass hydrometers areused in large works to ascertain its strength, andare sufficiently trustworthy for general purposes.In taking the specific gravity of sulphuric acid it isvery important to take the temperature into account,as it greatly influences the density. On removinga thermometer from the acid it rises to 75° or 80°Fahr.; by absorption of water it afterwards slowlyfalls to the temperature of the air. Again, if thethermometer has its bulb covered with a film ofwater, and be plunged into a strong acid, it will rise10° Fahr. more beyond the real temperature. Anelevation equal to 10° Fahr. diminishes the densityof oil of vitriol by 0-005: 1000 parts being heatedfrom 60° to 212° Fahr. becomes 1043 parts in volume,and the specific gravity, which was T848, falls to1-772, being equal to a dilution of 14 per cent, ofwater.

Nordhausen Sulphuric Acid.—Fuming Acid. (II 2 S 20 4 ?) A thick oily liquid, generally of a brown colour.It is produced from dry ferrous sulphate, which isplaced in a glazed earthenware or sometimes a greenglass retort, which is exposed to a nearly white heat.The distillate (sulphuric oxide) is received in asmall quantity of water, or better, in oil of vitriol,and forms a dark - coloured liquid of a specificgravity of about 1-9. It boils at 120° to 130° Fahr.When cooled, it deposits crystals of a compound ofH 2 S0 4 with SOg. It smokes when exposed to theair, from the escape of volatile sulphuric anhydride.When heated it gives off sulphurous oxide, andsulphuric oxide remains.

Fuming sulphuric acid is now chiefly manufac-tured in Bohemia , and is in great request as asolvent for indigo; it is also largely used in the

manufacture of alizarine. When the brown acid iskept at a temperature of 32° Fahr. it readily formscrystals, which are a definite compound of 2 atomsof anhydrous sulphuric acid, and 1 atom of water.The sulphuric anhydride may be separated from thebrown acid, by careful distillation in a retort, into adry and cold receiver. It passes over in drops, whichconcrete on cooling into a tenacious mass of crystals.

By careful management the calcined sulphate pro-duces sometimes up to 30 or 40 per cent, of acid.

It may be safely stated that up to 1730 allsulphuric acid produced for commerce in England,was made from copperas (ferrous sulphate). Theconsumption was small, and the price was abouttwo shillings per lb., or £220 per ton. The presentprice for similar acid is £4 10s. per ton.

Sulphur. —The next mode of making sulphuricacid was by the oxidation of sulphurous acid (pro-duced by burning sulphur) in presence of vapourof water. This was the suggestion of two French chemists, Lefevre and Lemery, who added nitrateof potash to the sulphur in burning it; and the pro-cess was adopted in England by Dr. Ward about1736, as follows:—The sulphur and nitrate of potashwere suspended on an iron tray in a large wide-mouthed glass globe, partly filled with water; themixture was set fire to by a red-hot iron, and thenthe mouth of the globe was closed. As soon as thecharge was burnt another was inserted and fired, andthis was repeated till the acid was found to be suf-ficiently strong, when it was removed into a glassretort and was concentrated. This acid, which wastermed “ oil of vitriol from the bell,” sold for twoshillings per lb., and was in much demand on accountof its purity. In 1746 Dr. Roebuck of Birmingham put up the first leaden chamber in England, whichwas employed as a substitute for glass globes. Itwas small in dimensions, being about 6 feetsquare, and the charges of sulphur and nitre wereburned in the chambers, much in the same way asin the glass globes. The success of this mode ofmaking acid was so great, that others were erectedat Preston Pans in Scotland , in 1749, by Roebuckand Garbett. Acid works were erected in London by Kingscate and Walker in 1772, and at Ecclesnear Manchester in 1783. (R. C. Claphaji).

In 1797 there were in Glasgow alone six or eightacid works, and the following is a note of the cost ofmanufacturing 950 bottles:—

25 tons of sulphur at £40,.£1000 0 0

7 tons oi nitre at £100,. ... 700 0 0

Coals,. 105 0 0

Wages and houses for workmen,. 250 0 0

Tear and wear,...,. 30 0 0

Rent and buildings,...* 70 0 0

Cartage,. 40 0 0

2195 0 0

142,500 lbs. of oil of vitriol at 6 \d. £3859 17 6

Less 10 per cent, discount,. 385 19 9

- 3473 17 9

Say the cost was £32 per ton,")and the selling price was > Profit 1278 17 9£54 per ton nett,,.)

(J. MacTear),