7 59 ini: to be tested, the latter is carried zifiers in construction from the balance the instrument when Gravity of Solids. ming the specific gravity of solids are meiples that all bodies immersed that liquid equal in volume to the and at the same time are buoyed up of the liquid displaced. The upward upon the body immersed causes the wen and is proportional to the density wegan then, which a body seems to suffer represents the weight of a volume of Domme of the body immersed. To me ar 15.6° C. (60° F.) has been chosen 3maren leedide and may be directly employe, for des upon which no solvent effect is pro te bonide must be used, as will ELT sold can be ascertained Trondst the first three terms of the DE TAIL. The weight of the Megan of the wood in air; thini tem 1 A 3. For solids soluble in water, whether heavier or lighter than that liquid; 4. For solids in powder form. For solids insoluble in, but heavier than water, several methods are available; of these, the direct method of weighing is the most accurate and generally employed. In place of the more expensive hydrostatic balance, any good sensitive prescription balance may be used; the only extra piece necessary being a small wooden or stiff wire bench as a support for the vessel of water, as shown in Fig. 42. For instance, a piece of Diagram showing the manner of weighing a solid body in a liquid. metal is found to weigh 258.75 grains in air; by means of a silken thread, or fine horse-hair, it is completely immersed in pure water and found to weigh 235.75 grains, the difference or loss of weight, 23 grains, representing the weight of a volume of water equal in volume to the 258.75 grains of metal. Dividing 258.75 by 23, the specific gravity of the metal is found to be 11.25. 20 10 Graduated cylinder. Another but less accurate method is to weigh the solid in metric weight and then place it in a graduated cylinder containing sufficient water to submerge the solid completely (see Fig. 43); the difference between the first height of the water and that after immersion of the solid indicates the volume of water displaced, and its corresponding weight is readily noted. Suppose a solid body weighing 7.5 Gm., placed into 40 Cc. of water, causes the latter to rise to 41.5 Cc., showing that 1.5 Cc. of water have been displaced, which weigh 1.5 Gm.; then, applying the rule, 7.51.5=5, the specific gravity of the solid. Since solid bodies will float indifferently in any liquid having the same specific gravity as themselves, advantage may be taken of this property to determine the specific gravity of solids. Hager recommends determining the specific gravity of fats by placing them in alcohol and then adding water until the fat floats about indifferently beneath the surface of the mixture; the specific gravity of the mixture is then taken in the usual way, preferably by means of a pycnometer, and this at the same time expresses the specific gravity of the solid. To ascertain the specific gravity of solids insoluble in, but lighter than water, it becomes necessary to insure their immersion in water by attaching to them some heavy substance, the weight of which in water must previously have been ascertained. Upon immersing the two bodies in water it will be observed that the weight of the two appears less than the weight of the heavy body alone, which is due to the fact that the volume of water equal to the volume of the lighter body is heavier than the latter, and therefore exerts a greater upward pressure on the heavy body, causing it to appear to lose weight. The difference between the weight of the heavy body in water and the united weight of the light and heavy bodies in water expresses the excess of weight of a volume of water over the weight of a like volume of the light body; in other words, it shows how much heavier a volume of water is than the same volume of the light body; to find the exact weight of a volume of water equal to the volume of the light body, this difference, or excess, must be added to the weight of the light body in air. Suppose a piece of cork weighs 62.5 grains in air; attached to a piece of metal which weighs 94 grains in water, the whole is found upon immersion in water to weigh 88 grains, or 6 grains less than the metal alone; adding 6 to 625 grains (the weight of the cork) we obtain 68.5 grains, the weight of the water displaced by the cork. The specific gravity of the cork is found by dividing 62.5 by 68.5 according to the general rule on page 46. The answer will be 0.9124+. For solids soluble in water some other liquid must be selected for immersion, in which the solid body is perfectly insoluble and of which the specific gravity is known; in other respects any of the preceding methods may be followed. In such cases the weight of the liquid displaced, having been ascertained, may be used to find the weight of a corresponding volume of water, and the latter then be divided into the weight of the solid; or the weight of the solid in air may be divided by the weight of the liquid displaced and the quotient then multiplied by the specific gravity of the liquid; by either method the specific gravity of the soluble substance will be obtained. To find the weight of a corresponding volume of water, divide the weight of the liquid displaced by its specific gravity, for the weights of equal volumes of two bodies are to each other directly proportional as their specific gravities. Example: A piece of alum weighs 125 grains in air; immersed in oil of turpentine having the specific gravity 0.860 it weighs 62 grains; 125 divided by 63 (the loss of weight) yields 1.984; oil of turpentine weighing only 0.86 as much as water, 1.984 must be multiplied by 0.860, which gives 1.7062+ as the specific gravity of the alum. Or the weight of a volume of water corresponding to the volume of oil of turpentine displaced may be found by dividing 63 by 0.86, which equals 73.256, and this divided into 125, the weight of the alum in air, also gives 1.7062+ as the specific gravity of the alum. Sometimes it is desirable to find the specific gravity of solids in powder form, as calomel, reduced iron, lead oxide, and the like; this is best done by using a flask or bottle known to hold a definite quantity of water, introducing a certain weight of the powder, and then filling with water and weighing the total contents; as two bodies cannot occupy the same space at the same time, it follows that the flask or bottle containing the powder cannot hold the same quantity of water as when empty, and this difference corresponds to the weight of water equal in volume to the powder. Suppose 100 grains of an insoluble powder are placed in a counterpoised 1000-grain bottle, the latter being then filled with pure water; if the total contents weigh 1088 grains, 12 grains of water have been displaced by the powder, for 1088-100 leaves 988, and, as the bottle is capable of holding 1000 grains of water, the difference 1000-988- - 12 must have been displaced. Then applying the rule, 8.333+ is found to be the specific gravity of the powder, as 100 ÷ 128.333+. Specific Volume. The term specific volume is used to define the ratio existing between the volumes of certain weights of bodies and the volume of the same weight of pure water; it is therefore the opposite of specific gravity. Specific volume is ascertained by dividing the specific gravity of a body into unity, and hence may be called the reciprocal of specific gravity; it may also be found by dividing the weight of a given volume of water by the weight of an equal volume of a liquid. Every pharmacist is aware that it will require vessels of different size to hold one pound of ether, water, glycerin, sulphuric acid, oil of turpentine, or chloroform, and it is often desirable to know in advance the volume of a given weight of a liquid; the weight in grammes of any liquid multiplied by the specific volume, or divided by the specific gravity, of that liquid at once expresses the actual volume in cubic centimeters. To find the volume of a given weight, avoirdupois or apothecaries', of a liquid, it becomes necessary first to ascertain the volume of a like weight of water, and then to multiply this by the specific volume, or to divide by the specific gravity of the liquid; or the given weight of a liquid may be divided at once by its specific gravity, which will yield the weight of a volume of water equal to the volume of the liquid, and then by finding the volume of such a weight of water the volume of the liquid is at once known. Examples: If the volume of 500 Gm. of alcohol U.S.P. is desired, divide 500 by 0.820, the specific gravity of the alcohol, and the quotient 609.75+ will be the answer in cubic centimeters. To find the volume of 8 ounces of official glycerin (apothecaries' weight) it is necessary to multiply by 480, the number of grains in 1 ounce, and then divide the product by 455.7, the number of grains in one U. S. fluidounce of water, the quotient (480 x 83840; 3840455.7 8.427), 8.427, represents the number of fluidounces contained in the same weight of water; 8.427 then divided by 1.25, the specific gravity of the glycerin, yields 6.7416 fluidounces as the volume of 8 troy ounces of glycerin. How large a bottle is required to hold one pound of chloroform of 1.490 specific gravity? One pound avoirdupois is equal to 7000 grains, and 7000 1.490 4697.986, the weight in grains of a volume of water equal to the chloroform; then 4697.986 455.7 10.309, or very nearly 103 fluidounces. = = Adjustment of Specific Gravity and Percentages. While the adjustment of percentages in liquids as well as solids presents no difficulties, the reduction of liquids from a higher to a lower specific gravity is not quite so easily accomplished, since specific gravity is but the expression of the relation between volume and weight, and condensation of volume frequently occurs as the result of a mixture of two liquids. Two very simple rules, or formulas, have been published for the adjustment of specific gravities of liquids, by volume and by weight; but absolutely accurate results are only possible when no contraction of volume takes place; in the majority of cases the condensation of volume is but very slight, and for ordinary purposes may be ignored. It is well known that the weights of equal volumes of two liquids are to each other directly proportional as the specific gravities of these liquids; therefore, the weight of a liquid divided by its specific gravity represents a weight of water equal in volume to the weight of that liquid. It is also well known that the volumes of equal weights of two liquids are to each other inversely proportional as the specific gravities of these liquids; therefore, the volume of a liquid multiplied by its specific gravity represents a volume of water equal in weight to the volume. of that liquid. The well-known process of alligation is admirably adapted to the adjustment of specific gravities of liquids by volume, but is unsuited to adjustment by weight. When two liquids of |