250 SULPHATE OF AMMONIA.

perature. I do not find that the gummate is redissolved by an excess of water, asTrommer affirms.

Starch and tragacants comport like gnm, in which respect I agree with Trommer.Starch, however, possesses already a perfect criterion, in iodine water. Mr. Trommersays, that solution of dextrine affords a deep glue-colored liquid, without a trace olprecipitate; and that when his mixture is heated to 85° C., it deposites red grains ofprotoxide of copper, soluble in muriatic acid. I think these phenomena are dependant,in some measure, upon the degree of alkaline excess in the mixture. I find, the solu-tion of dextrine, treated in my way, hardly changes in the cold; but when he’atedslightly, it becomes green, and by brisk boiling an olive tint is produced. It thus be-trays its tendency of transition into sugar.

Solution of cane-sugar, similarly treated, undergoes no change in the cold at the endof two days; and very little change of color even at a boiling heat, if not too concen-trated. Cane-sugar, treated by Trommer in his way, becomes of a deep blue; it canbe boiled by potash in excess, without any separation of orange-red oxide of copper.

Starch or grape-sugar has a marvellous power of reducing the green hydrate ofcopper to the orange oxide. I find, however, that it will not act upon the pure bluehydrate, even when recently precipitated; it needs the addition, in every case, of asmall portion of alkali. Yet ammonia does not seem to serve the purpose; for, inusing the ammonia-sulphate of copper, in solution, I obtained unsatisfactory resultswith the above vegetable products.

The black Oxide of copper is not affected by being boiled in solution of starch-sugar.

“ If solution of grape-sugar,” says Trommer, “ and potash, be treated with a solutionof sulphate of copper, till the separated hydrate is redissolved, a precipitate of redoxide will soon take place, at common temperatures, but it immediately forms, if the

mixture is heated. A liquid containing_I_of grape-sugar, even one millionth

part,” says he, “ gives a perceptible tinge (orange), if the light is let fall upon it.” Toobtain such a minute result, very great nicety must be used in the dose of alkali, whichI have found it extremely difficult to hit. With my regulated alkaline mixture, how-ever, I never fail of discovering an exceedingly small proportion of starch-sugar, evenwhen mixed with Muscovado sugar; and thus an excellent method is afforded of de-tecting the frauds of the grocers.

I find that manna deoxidizes the green hydrate of copper slowly when heated, butnot nearly to the same extent as grape-sugar, which reduces it rapidly to the orang eoxide.

If an excess of the hydrate of copper test be used, there will be a deposite of greenhydrate at the bottom of the vessel, under the orange oxide.

To apply these researches to the sugar of diabetic urine : This should first beboiled briskly to decompose the urea, and to dissipate its elements in the form of am-monia, as well as to concentrate the saccharine matter, whereby the test becomes m° reefficacious. Then add to the boiling urine, in a few drops at a time, the cupreousmixture, containing a known quantity of sulphate of copper, till the whole assumes agreenish tint, and continue the heat until the color becomes bright orange. Shouldit remain green, it is a proof that more hydrate of copper has been introduced than hasbeen equivalent to the deoxidizing power of the starch-sugar. I have found that onegrain of sulphate of copper in solution, supersaturated very slightly with potash, is de-composed with the production of orange protoxide, by about 3 grains of potato-siiga 1 ';or, more exactly, 30 parts of the said sulphate, in the state of an alkaline hydrate ofcopper, pass altogether into the state of orange oxide, by means of 100 parts of granularstarch-sugar. Thus, for every 3 grains of sulphate so changed, 10 grains of sugarmay be estimated to exist in diabetic urine.

Acetate of copper may be used in the above experiments, but it is not so good as thesulphate. The chloride of copper does not answer.

Specific gravity is also an important criterion, applied to sugars; that of the cantand beet-root is 1-577 ; that of starch-sugar, in crystalline tufts, is 1-39, or perhaps1-40, as it varies a little with its state of dryness. At 1-342, syrup of the cane contains70 per cent, of sugar; at the same density, syrup of starch-sugar contains 75£ per cen •of concrete matter, dried at 260° F., and therefore freed from the 10 per cent, owater which it contains in the granular state. Thus, another distinction is obtain*-between the two sugars, in the relative densities of their solutions, at like saccliaricontents per cent. .

SULPHATE OF AMMONIA. This salt, now so extensively used in preparingartificial manures and imitations of guano, for farmers, is made of great purity, an . j ean economical rate, by the patent process of Mr. Oroll, described under the artiGas. A mixture of 10 per cent, of this sulphate with 20 of bone-dust, someand farmyard manure, will form a very fertilizing compost, applicable to a grvariety of soils.