GUMS.

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importance than is often imagined; for, supposing a manufafturer to requireannually a given quantity of gum of first rate quality, and to pay for thatquantity, say ^3520, if the viscosity of the gum were reduced by one-tenth, it isclear that this would necessitate an outlay of £352 more. Several instrumentshave been devised for measuring the viscosity of solutions of gum and otherviscous materials, and of these the least expensive and most simple appearsto be a glass funnel, the tube of which is drawn out to a fine point. Solutionsof gum are made in definite proportions, and the funnel having been filled, thetime that the several solutions take to run through is accurately noted, thisoperation being shorter or longer according to the degree of viscosity of thesolution under treatment. M. Steilmann’s viscosimeter consists of two hollowglass cylinders, placed side by side, one of which is filled with pure water,and the other with the solutions to be tested. Into each of these cylindricalglasses (which are precisely similar) metallic balls can be let down. Theseballs are suspended by silk threads, and move freely over pulleys; they are,however, partly counterpoised by means of weights. If the viscosity of theliquids placed in the glass cylinders be equal, the metal balls will descendwith the same speed, provided, of course, that they are of the same sizeand weight; but if one of the cylinders contain water, and the other asolution of gum, the ball will sink into the latter more slowly than into theformer. The descent of the balls, when nearly at the bottom of the cylinder,is stopped by a peculiar mechanical arrangement. M. Steilmann’s apparatusis in many respefts an excellent one, but it is too complicated to be of greatpractical use to those who require to test several samples of gum in a shortspace of time. It should be borne in mind that although a solution may bemade of accurately weighed quantities of gum and water, the degree ofviscosity of such a solution is affedted by the temperature of the water and ofthe room in which the experiment is made. It is therefore necessary thatthese experiments should always be made at the same temperature, 59° F.(15° C.), and it is also advisable to be provided with a freshly-made solutionof best quality gum that may be used as a standard of comparison.

Gum Tragacanth is the produce of the Astragalus vents, a tree growingin Persia, Armenia, and Asia Minor. It is a white or yellow looking substance,and is not really soluble in water, as it only swells in it, yielding a thickmucilage. It contains on an average about half its weight of soluble arabine,but consists principally of what is often called bassorine. Gum tragacanthalways contains some starch. Before being used it is soaked in cold waterfor twenty-four hours, and afterwards boiled from four to six hours until athick homogeneous solution is obtained. The quantity of gum to 35 ozs. ofwater varies from about 930 to 1530 grs. Though the solution made asdescribed is very thick and nearly colourless, it is less cohesive than gumsolution, and cannot therefore replace it. When gum tragacanth is boiledwith water, under a pressure of from four to five atmospheres, it yields inabout twenty minutes a thick solution. To test the viscosity of this gum279 grs. are taken upon 17^ ozs. of water; the fluid is boiled, and when ithas cooled down to 59° F. (15° C.) its viscosity is compared with that of asolution of the same strength made from a good sample of the gum.

The mucilage produced by steeping linseed, the seeds of quinces, andcarragheen moss for some time in warm water, also affords a thickening