CONCENTRATION, in chemistry, the act of increasing the strength of fluids, which are rendered stronger by abstract ing a portion of the mere menstruum. This is generally effected by evaporation, where the menstruum is driven off at a lower heat than is required to drive off the substance with which it is united. Thus, dilute sulphuric acid may be con sidered as a mixture of the real acid with ; and by applying a certain heat the water may be evaporized, leaving the acid behind in a state of concentration. When concentrated as much as possible, its specific gravity is about twice as great as that of water ; but it can rarely be ob tained denser than 1.85. When concen trated to 2.000 it contains a considerable portion of water, as has been proved by combining it with barytes or potash, in which case water remains behind, and does not enter into the combination. Again, vinegar consists of an acid and wa ter, and brandy of alcohol and water ; and in proportion as the acid and alcohol are freed from the water, they are said to be more or less concentrated. This may be performed, (1.) either by simple distilla tion, in which case the acid or spirit comes over first, leaving the water behind ; or, (2,) by exposing the vinegar or brandy to severe frost, when the water will be fro zen, and the acid or alcohol will be found in a state of concentration in the middle of the ice ; the greater the cold the high er the state of concentration. M. Lowitz
has found that the acid, however concen trated, congeals at 22°. Sulphuric acid, on the other hand, exposed to a much less severe cold, crystallizes, and to effect this it must not be greatly concentrated. (3.) Another mode of concentrating the a cetic acid is by distilling acetate of copper reduced to a powder in a retort. At first there comes over a liquid nearly colour less, and almost insipid, and afterwards a highly concentrated acid, tinged with green ; but being distilled a second time in a moderate heat, it is colourless, trans parent, exceedingly pungent, and con centrated. (4.) The most perfect method of obtaining this acid in a concentrated state was discovered by Mr. Lowitz, of Petersburgh. It is thus : distil a mixture of three parts of acetate of potash, and four parts of sulphuric acid, till the ace tic acid has come over into the receiver. To separate it from the sulphuric acid, with which it is slightly contaminated, it must be distilled over a portion of ace tate of barytes.