UUR. 



suLi'iin:. 



sulphurous and nitrous acid*, atmospheric air, and watery vapour. 

 Now, when dry sulphurous acid gaa and dry nitrous ac-id ROS arc mixed 

 together, no action occurs between them; but when a little moistun 

 U added. whit* crystalline compound of (ajptrario add, hyponHroni 

 acid, and water is formed; and when this {alls into ilu- V..IM .! tl. 

 chamber, or oomea into contact with steam, which is (or this purpose 

 into the chamber, it U instantly decompoeed, the sulphuric acid 

 U dissolved, and nitrous acid and nitric oxide gases escape with effer- 

 vescence. The nitrous acid thus set free, a well as that reproduced 

 by the nitric oxide uniting with the oxygen of the atmosphere, U again 

 intermixed with sulphurous acid and moisture, and thus gives rise to 

 a second portion of the crystalline body, which undergoes the same 

 change as the first ; and this operation is repeated until the water at 

 the bottom of the lead-chambers u sufficiently acid to be removed for 

 ulterior operations. The amount of nitric acid required in this ope- 

 i< of course exceedingly small, inasmuch as the nitric oxide 

 contained in it is not consumed, but acts only as a carrier of oxygen 



.lie air to the sulphurous acid. Some nitric oxide is, li< 

 conveyed out of the chambers by the escaping nitrogen of the air, and 

 >ost works lost. A few manufacturers cause the escaping gases 

 to pass over strong sulphuric acid that is trickling through a coke 

 column, by which the nitric oxide is dissolved and subsequently 

 recovered from the liquid by exposure to a stream of sulphurous acid 

 in a second similar coke column. 



It thus appears that sulphur during combustion can combine only 

 with sufficient oxygen to become sulphurous acid ; but what" is curious 

 is, that sulphurous acid becomes sulphuric acid by taking oxygen 

 from nitrous acid, the nitric oxide of which appears nevertheless to 

 have a stronger affinity for oxygen, since it can take that element 

 rapidly from the air, which sulphurous acid cannot. The first attempt 

 at explaining the mode in which nitric acid acts in this operation was 

 made by MM. Clement and Desormes : it was subsequently further 

 explained by Davy and other chemists. 



Of late years also sulphuric acid has been made from iron pyrites, the 

 hulplmrouB acid being formed by combustion, and converted into 

 .sulphuric by the agency of nitrous acid, in the manner .-dr.-ady 

 il>ed. 



When the sulphuric acid in the chambers has acquired a density of 

 about 1-6, it is drawn off and further concentrated in open leaden 

 vessels by heat ; after this it is again removed either, to glass or platina 

 -. and heated till it has acquired a density of about 1-846. This 

 i.- th<n the sulphuric acid, or oil of vitriol, of commerce, composed of 

 one equivalent of sulphuric acid and one equivalent of water (HO, 

 SO). 



This acid is a limpid, inodorous, colourless fluid, of an oily con- 

 sistence. It boils at about 620, and distils over unchanged ; the 

 boiling-point diminishes with dilution : thus, when of specific gravity 

 178 it boils at 435, and when T65 only at 350, the concentrated acid 

 - at 15, but when it contains two equivalents of water instead 

 .dy one, and has a specific gravity of 1*78, it freezes at 40. 



Sulphuric acid is intensely caustic and acrid, and readily decomposes 

 animal and vegetable fibre ; even when diluted to a very great extent 

 it has an extremely sour taste, and turns vegetable blues strongly red : 

 on tin; other hand, when concentrated, it turns turmeric-paper of a 

 lour, an the alkalies do ; but the effect is not permanent, for 

 it in removed by water. Its aflinity for water is very great, attracting 

 it so readily from the air that in moist weather three parts increase to 

 four in "J4 hours, and by longer exposure the quantity is increased. 

 When (suddenly mixed with water, much heat is evolved, and, on 

 cooling, condensation is found to have taken place, the two fluids occu- 

 less space than before mixture. When sulphuric acid is mixed 

 in certain proportions with snow, heat is given out, or cold generated, 

 according to the quantities employed : thus four parts of acid and one 

 of snow evolve heat, but four of snow and one of acid occasion cold. 



Sulphuric acid is employed for a vast number of purposes : thus, on 

 account of its great chemical power, it is used for the purpose of sepa- 

 rating other acids from bases, as in preparing nitric, hydrochloric, 

 acetic, phosphoric, and carbonic acids, &c. It is also used in preparing 

 sulphates, a class of salts we shall presently again refer to. Perhaps 

 the greatest consumption of sulphuric acid is in the decomposition ol 

 salt at alkali works where carbonate of soda is manufactured. 



The strength of sulphuric acid is readily ascertained by taking its 

 specific gravity and referring to such a table as the following, con 

 structed by Ure : 



Spcclnc 



gravity. 



8460 



8415 



8366 



8288 



; i 



7901 



7728 



7540 



7315 



7080 



1-6810 



1-G624 



SO, in Percentage 

 100 part*, of HO, SO,. 



81-54 

 79-90 

 78-28 

 76-65 

 75-02 

 73-39 

 71-75 

 70-12 

 68-49 



Utl 



. -. N 

 61-97 



100 

 98 

 06 

 94 

 02 

 00 

 88 

 86 

 84 

 82 

 80 

 78 

 76 



-:- 

 gravity. 



3697 



3530 



3345 



111 . 

 : '" i 



2826 



MM 



2490 



2334 



2184 



2032 



1870 



1706 



The salts which sulphuric acid forms with various bases are t 

 l/ikiiti.t, n'f/ni-fnlphatei, or la-ulphata, &c., according I" cin-iini- 

 Htances. They are a very important clas of .--aline bodies, and 1 1 

 most use will be found described under their respective \a-< s. With 

 sulphuric anhydride, dry ammoniacal gas forms large t: in 

 crystals, containing NHj.SO,, and termed nilphatamvum .- by l"tig 

 boiling with water, it is converted into sulphate of amm"nia 

 (NH.O,SO S ). 



According to the binary theory of the constitution of salts, sulphate* 

 are not combinations of the basic oxide and sulphuric acid, but of a 

 hypothetical body, fulphion (SO,), with the metal, or radii :<}, of tin- 

 base : thus, sulphate of soda (NaO, SO S ) is sulphioniile of . 

 (Na, SOJ, and sulphuric acid (H, SO.) tulphionide of Ay 

 There are, however, several objections to this view of the constitution 

 of sulphates. 



Sulphuric acid in its concentrated state, and at common tempe- 

 ratures, acts only slightly, if at all, on the metals ; but when they are 

 heated together, the acid is generally decomposed, sulphurous acid and 

 a sulphate of metallic oxide being produced : thus, when copper is 

 in concentrated sulphuric acid, the acid yields one of its three 

 equivalents of oxygen to the copper, which becomes protoxide ; while 

 the sulphur combined with two equivalents of oxygen is given off in 

 the state of sulphurous acid; and this, as already indicated, i 

 the best methods of procuring sulphurous acid. When, on tin 

 hand, sulphuric acid is diluted, it has no action, even wh. u 

 copper ; but on zinc, iron, and such other metals as readily decompose 

 water, it acts with great readiness : the metal, being oxidised by tin'; 

 oxygen of the decomposed water, is dissolved by the add, while th 

 hydrogen of the water is given out in the gaseous state; by this 

 operation, then, we procure a metallic sulphate and hydrogen ;_ 



Sulphuric acid and all sulphates are decomposed by the salts of 

 baryta and of lead, minute quantities either of the acid or soluble salts 

 being rendered evident by the formation of a dense white precipitate 

 either of sulphate of baryta or lead ; 116-5 parts of the former or 115'(J 

 parts of the latter sulphate, when dry, indicate 40 ports of anhydrous 

 sulphuric acid. 



Commercial sulphuric acid generally contains sulphate of lend . - 

 from the \e.--i'U used in its manufacture; it is nearly all preoi 

 .is a white powder on diluting the add with water. It frequent 

 contains traces of arsenic derived from the pyrites; in thi 

 sulphuretted hydrogen given a yellow precipitate win 

 the diluted acid, or the contamination may be detected by Mai.-h.; 

 test. StiKill quantities of nitric and sulphurous acids are also sometimes 

 present in common sulphuric acid. If required to be purified and 

 concentrated, it is boiled and distilled. As lead would melt at the 

 heat here employed, and as most other common substances would In; 

 corroded, platinum is often employed as a material for the still, at a 

 heavy expense. Gloss is another material employed for sulphuric a. -id 

 stills. When the acid has been condensed to a specific gravity in arly 

 double that of water, it is ready for sale. 



Ifyposulphurous Acid (HO, S,0j). />/////''!. arid. In IS] 7 l>r. 

 Thomson inferred the existence of an acid of sulphnr.in the salts called 

 siil/Jiiirtttedtulphita: this acid and its compounds have been particu- 

 larly examined by Sir John Herschel. 



Hyposulphurous acid has not been obtained in a separate state, but 

 its composition has been determined to be in accordance with tin.; 

 above formula. 



This acid is procured by dissolving zinc or iron in close vessels in an 

 aqueous solution of sulphurous acid : solution is effected in this acid 

 without the evolution of any gas, which hardly happens in any other 

 case: the metals thus dissolved form crystallisable salts, which, wln-n 

 decomposed by other acids, yield sulphurous acid and sulphur, pre- 

 viously existing in the proportions above stated, and constituting 

 hyposulphurous acid: this acid is also formed when snlphit 

 digested in eloi*e vessels with sulphur, in which case the stilphu. 

 half the oxygen of the sulphurous acid; when ii> Ived in 



sulphurous acid, it takes half the oxygen of the sulphurous a. -id, which, 

 by this loss becomes hyposulphurous acid, and, combining with the, 

 oxide of iron formed, they constitute hyposulphite of iron. 



Most of the salt* containing hyposulphurous acid, or the hyposul- 

 phites, sre unimportant; the acid undergoes decomposition when th. \ 

 are strongly heated or acted upon by an 



//'/tuulpkite of soda (NaO, S..O 2 + 5 Aq.), in solution, is largeh 

 in photography to "fix," or render permanently unalterable the photo- 



