and the solution is at once made strong enough togive a large crop of crystals on cooling.
Before proceeding to consider the manufactureof soda from sodium sulphate, the other product ofthe action of sulphuric acid on salt will be noticedthus, is:—
HYDROCHLORIC ACID — Clorhjdric Acid ,Muriatic Acid , Spirit of Salt . Symbol HC1. AcidIlydrochlorique, French; Salzsaure , German.
H, 1-0 . 2-74
36-5 100-00
Nearly all the hydrochloric acid now producedin England is obtained from the decomposition ofcommon salt, so extensively used in alkali works,where the acid is chiefly employed for the produc-tion of chlorine, bleaching powder, or chlorate ofpotash. To give some idea as to the enormousextent to which hydrochloric acid is now produced,the writer may mention, that on the river Tyne alone there is produced about 300,000 tons annually,and in the United Kingdom probably altogether notfar short of a million tons annually. It may beinteresting to glance back for some years to noticehow this important branch of manufacture has de-veloped from a very small beginning. As recentlyeven as one hundred years ago chlorine was notused in the arts, and our British -made linens andcalicoes, &e., after they were boiled in lyes madefrom Scotch kelp, were then saturated with sourmilk, and were simply exposed for a long time tothe action of the sun and air to bleach them. Buton account of the uncertain climate of this countryit was found to be necessary to send the best clothsto Holland, and after a summer’s absence and ex-posure to a brighter sun, they were returned toEngland for consumption. White paper suitable towrite upon could only at that time be producedfrom the whitest rags, as no chemical methods forbleaching inferior materials were then in practice.Long before hydrochloric acid was made by thepresent methods, there is evidence to show thatit was occasionally produced by heating clay andsalt together in a metal retort, when a small part ofthe salt was decomposed with escape of hydro-chloric acid, or, as it was then called, “marine acid.”A nearly similar process was pursued in mixingsulphate of iron (or copperas) and salt, and subject-ing the mixture to heat in a retort, when the “marineacid” was also produced (R. C. Clapham).
It was not till about 1789 that this acid began tobe produced by the decomposition of salt with sul-phuric acid, on a tolerably large scale, and this wasfirst done in France during the French Revolution ;but it was not for many years afterwards that hydro-chloric acid began to be made in a large way in Eng-land. In 1823 the heavy excise duty on salt, whichhad varied in amount from £10 to £36 per ton ofsalt, was repealed by the Government, and this atonce gave a stimulus to the establishment of alkaliworks, both on the river Tyne, in Lancashire , and inGlasgow and elsewhere. For several years after the
above date there was no extensive use found forhydrochloric acid, and all the fumes from the de-composition of salt were allowed to escape into theair from the short chimneys then in use, and werefound to do much injury to surrounding vegetation.At this time, however, the works were compara-tively small, and it was not considered necessary tomake any attempts to condense the gas; but fromthe continued increase of demand for alkalies andfor bleaching powder the question of condensationbecame very important and pressing on manufac-turers. Various methods were attempted at first.The early experiments in this direction on the Tyne were made at Walker Alkali Works in 1827; largewooden chambers or boxes were erected, throughwhich the gas was made to pass, and in some casesunderground cellars or tanks were substituted, andin both jets of water were forced in amongst thegas. In 1835 W. S. Losir, at the same works, putdown long underground flues, into which water wasforced by means of an engine. The next thing wasthe erection of towers constructed of stone and filledwith glass or flints, through which the hydrochloric(in alkali works always termed muriatic ) acidgas ascended, at the same time meeting a stream ofwater; but still for the most part all these attemptswere failures, or at least were imperfect, and to getover the difficulty high chimneys were erected, whichare to this day a peculiar characteristic of chemicalworks, the chief object at that time being to spreadthis injurious gas over a large surface. It was inthese difficulties that the late William Gossage, ofLiverpool, took out a patent in 1836 for the con-struction of condensers packed with coke, throughwhich the gas passed, being at the same time subjectto a spray or shower of cold water. His methodwas generally approved by manufacturers, and underall ordinary circumstances these condensers are cap-able of effecting almost a complete condensation ofthe hydrochloric acid gas that is now produced soextensively in chemical works. But it was not till1843 that good condensation was carried out, and ittook some years after this date to bring about theperfect system which is now adopted in nearly allchemical works. The escape of small quantities ofgas, both from the condensers and the internalarrangements of the works, still, however, continued,and caused considerable damage to the surroundingfields, trees, and gardens.
In 1863 an Act of Parliament was passed, calledthe “ Alkali Act,” which fixed the maximum escapeof gas from any work at 5 per cent., and at the sametime appointed inspectors under the Board of Trade.This Act remained in force till 1874, when a newAct was passed, containing more stringent clausesas to the escape, and fixing the maximum quantityat 0-2 grains per cubic foot of “ air, smoke, or chim-ney gases escaping from the works into the atmos-phere.” These Acts have now been on trial eversince that time; and no difference of opinion existsas to the advantages which have been derivedboth by the manufacturer and the general publicby their enactment. Much useful information