What is "double salt"

Salt \Salt\, n. [AS. sealt; akin to OS. & OFries. salt, D. zout, G. salz, Icel., Sw., & Dan. salt, L. sal, Gr. ?, Russ. sole, Ir. & Gael. salann, W. halen, of unknown origin. Cf. Sal, Salad, Salary, Saline, Sauce, Sausage.]

1. The chloride of sodium, a substance used for seasoning food, for the preservation of meat, etc. It is found native in the earth, and is also produced, by evaporation and crystallization, from sea water and other water impregnated with saline particles.

2. Hence, flavor; taste; savor; smack; seasoning.

   Though we are justices and doctors and churchmen . . . we have some salt of our youth in us.
   --Shak.

3. Hence, also, piquancy; wit; sense; as, Attic salt.

4. A dish for salt at table; a saltcellar.

   I out and bought some things; among others, a dozen of silver salts.
   --Pepys.

5. A sailor; -- usually qualified by old. [Colloq.]

   Around the door are generally to be seen, laughing and gossiping, clusters of old salts.
   --Hawthorne.

6. (Chem.) The neutral compound formed by the union of an acid and a base; thus, sulphuric acid and iron form the salt sulphate of iron or green vitriol.

   Note: Except in case of ammonium salts, accurately speaking, it is the acid radical which unites with the base or basic radical, with the elimination of hydrogen, of water, or of analogous compounds as side products. In the case of diacid and triacid bases, and of dibasic and tribasic acids, the mutual neutralization may vary in degree, producing respectively basic, neutral, or acid salts. See Phrases below.

7. Fig.: That which preserves from corruption or error; that which purifies; a corrective; an antiseptic; also, an allowance or deduction; as, his statements must be taken with a grain of salt.

   Ye are the salt of the earth.
   --Matt. v. 13.

8. pl. Any mineral salt used as an aperient or cathartic, especially Epsom salts, Rochelle salt, or Glauber's salt.

9. pl. Marshes flooded by the tide. [Prov. Eng.] Above the salt, Below the salt, phrases which have survived the old custom, in the houses of people of rank, of placing a large saltcellar near the middle of a long table, the places above which were assigned to the guests of distinction, and those below to dependents, inferiors, and poor relations. See Saltfoot. His fashion is not to take knowledge of him that is beneath him in clothes. He never drinks below the salt. --B. Jonson. Acid salt (Chem.)

   1. A salt derived from an acid which has several replaceable hydrogen atoms which are only partially exchanged for metallic atoms or basic radicals; as, acid potassium sulphate is an acid salt.

   2. A salt, whatever its constitution, which merely gives an acid reaction; thus, copper sulphate, which is composed of a strong acid united with a weak base, is an acid salt in this sense, though theoretically it is a neutral salt. Alkaline salt (Chem.), a salt which gives an alkaline reaction, as sodium carbonate. Amphid salt (Old Chem.), a salt of the oxy type, formerly regarded as composed of two oxides, an acid and a basic oxide. [Obsolescent] Basic salt (Chem.)

      1. A salt which contains more of the basic constituent than is required to neutralize the acid.

      2. An alkaline salt. Binary salt (Chem.), a salt of the oxy type conveniently regarded as composed of two ingredients (analogously to a haloid salt), viz., a metal and an acid radical. Double salt (Chem.), a salt regarded as formed by the union of two distinct salts, as common alum, potassium aluminium sulphate. See under Double. Epsom salts. See in the Vocabulary. Essential salt (Old Chem.), a salt obtained by crystallizing plant juices. Ethereal salt. (Chem.) See under Ethereal. Glauber's salt or Glauber's salts. See in Vocabulary. Haloid salt (Chem.), a simple salt of a halogen acid, as sodium chloride. Microcosmic salt. (Chem.). See under Microcosmic. Neutral salt. (Chem.)

         1. A salt in which the acid and base (in theory) neutralize each other.

         2. A salt which gives a neutral reaction. Oxy salt (Chem.), a salt derived from an oxygen acid. Per salt (Old Chem.), a salt supposed to be derived from a peroxide base or analogous compound. [Obs.] Permanent salt, a salt which undergoes no change on exposure to the air. Proto salt (Chem.), a salt derived from a protoxide base or analogous compound. Rochelle salt. See under Rochelle. Salt of amber (Old Chem.), succinic acid. Salt of colcothar (Old Chem.), green vitriol, or sulphate of iron. Salt of hartshorn. (Old Chem.)

            1. Sal ammoniac, or ammonium chloride.

            2. Ammonium carbonate. Cf. Spirit of hartshorn, under Hartshorn.

               Salt of lemons. (Chem.) See Salt of sorrel, below.

               Salt of Saturn (Old Chem.), sugar of lead; lead acetate; -- the alchemical name of lead being Saturn.

               Salt of Seignette. Same as Rochelle salt.

               Salt of soda (Old Chem.), sodium carbonate.

               Salt of sorrel (Old Chem.), acid potassium oxalate, or potassium quadroxalate, used as a solvent for ink stains; -- so called because found in the sorrel, or Oxalis. Also sometimes inaccurately called salt of lemon.

               Salt of tartar (Old Chem.), potassium carbonate; -- so called because formerly made by heating cream of tartar, or potassium tartrate. [Obs.]

               Salt of Venus (Old Chem.), blue vitriol; copper sulphate; -- the alchemical name of copper being Venus.

               Salt of wisdom. See Alembroth.

               Sedative salt (Old Med. Chem.), boric acid.

               Sesqui salt (Chem.), a salt derived from a sesquioxide base or analogous compound.

               Spirit of salt. (Chem.) See under Spirit.

               Sulpho salt (Chem.), a salt analogous to an oxy salt, but containing sulphur in place of oxygen.

Double \Dou"ble\ (d[u^]b"'l), a. [OE. doble, duble, double, OF. doble, duble, double, F. double, fr. L. duplus, fr. the root of duo two, and perh. that of plenus full; akin to Gr. diplo`os double. See Two, and Full, and cf. Diploma, Duple.]

1. Twofold; multiplied by two; increased by its equivalent; made twice as large or as much, etc.

   Let a double portion of thy spirit be upon me. -- 2 Kings ii. 9.

   Darkness and tempest make a double night.
   --Dryden.

2. Being in pairs; presenting two of a kind, or two in a set together; coupled.

   [Let] The swan, on still St. Mary's lake, Float double, swan and shadow.
   --Wordsworth.

3. Divided into two; acting two parts, one openly and the other secretly; equivocal; deceitful; insincere.

   With a double heart do they speak. -- Ps. xii. 2.

4. (Bot.) Having the petals in a flower considerably increased beyond the natural number, usually as the result of cultivation and the expense of the stamens, or stamens and pistils. The white water lily and some other plants have their blossoms naturally double. Note: Double is often used as the first part of a compound word, generally denoting two ways, or twice the number, quantity, force, etc., twofold, or having two. Double base, or Double bass (Mus.), the largest and lowest-toned instrument in the violin form; the contrabasso or violone. Double convex. See under Convex. Double counterpoint (Mus.), that species of counterpoint or composition, in which two of the parts may be inverted, by setting one of them an octave higher or lower. Double court (Lawn Tennis), a court laid out for four players, two on each side. Double dagger (Print.), a reference mark ([dag]) next to the dagger ([dagger]) in order; a diesis. Double drum (Mus.), a large drum that is beaten at both ends. Double eagle, a gold coin of the United States having the value of 20 dollars. Double entry. See under Bookkeeping. Double floor (Arch.), a floor in which binding joists support flooring joists above and ceiling joists below. See Illust. of Double-framed floor. Double flower. See Double, a., 4. Double-framed floor (Arch.), a double floor having girders into which the binding joists are framed. Double fugue (Mus.), a fugue on two subjects. Double letter.

   1. (Print.) Two letters on one shank; a ligature.

   2. A mail requiring double postage. Double note (Mus.), a note of double the length of the semibreve; a breve. See Breve. Double octave (Mus.), an interval composed of two octaves, or fifteen notes, in diatonic progression; a fifteenth. Double pica. See under Pica. Double play (Baseball), a play by which two players are put out at the same time. Double plea (Law), a plea alleging several matters in answer to the declaration, where either of such matters alone would be a sufficient bar to the action. --Stephen. Double point (Geom.), a point of a curve at which two branches cross each other. Conjugate or isolated points of a curve are called double points, since they possess most of the properties of double points (see Conjugate). They are also called acnodes, and those points where the branches of the curve really cross are called crunodes. The extremity of a cusp is also a double point. Double quarrel. (Eccl. Law) See Duplex querela, under Duplex. Double refraction. (Opt.) See Refraction. Double salt. (Chem.)

      1. A mixed salt of any polybasic acid which has been saturated by different bases or basic radicals, as the double carbonate of sodium and potassium, NaKCO3.6H2O.

      2. A molecular combination of two distinct salts, as common alum, which consists of the sulphate of aluminium, and the sulphate of potassium or ammonium.

         Double shuffle, a low, noisy dance.

         Double standard (Polit. Econ.), a double standard of monetary values; i. e., a gold standard and a silver standard, both of which are made legal tender.

         Double star (Astron.), two stars so near to each other as to be seen separate only by means of a telescope. Such stars may be only optically near to each other, or may be physically connected so that they revolve round their common center of gravity, and in the latter case are called also binary stars.

         Double time (Mil.). Same as Double-quick.

         Double window, a window having two sets of glazed sashes with an air space between them.

n. (context chemistry English) A solid solution of two simple salts, often in a definite proportion

n. a solution of two simple salts that forms a single substance on crystallization

Double salts are salts containing more than one cation or anion, and are obtained by combination of two different salts which were crystallized in the same regular ionic lattice. Examples of double salts include alums (with the general formula MM[SO]·12HO) or Tutton's salt (with the general formula [M]M[SO]·6HO). Other examples are potassium sodium tartrate, ammonium iron(II) sulfate and bromlite.

Note that double salts should not be confused with a complex. When dissolved in water, a double salt completely dissociates into simple ions while complexes do not; the complex ion remains unchanged. For example, KCeF is a double salt and gives K, Ce and F ions when dissolved in water, whereas K[YbI] is a complex salt and contains the discrete [YbI] ion which remains intact in aqueous solutions. It is therefore important to indicate the complex ion by adding a square bracket "[ ]" around it.

In general, the properties of the double salt formed will not be the same as the properties of its component single salts.