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but with two parallel beams. Employed for weighing liquids, etc., the outside beam being used to tare the bottle or jar.

4. COMPOUND LEVER BALANCES.—Well shown in Fairbanks' platform scales, used for druggists' counters and sometimes for prescription scales. Trömner has an excellent scale for weighing liquids on this principle.

5. TORSION BALANCES.—A compound beam is balanced and supported upon an immovable centre frame, upon which a flattened gold wire is stretched with powerful tension; the beam is prevented from slipping out of place, and the torsion is secured, by the gold wire being firmly fastened to the under side of the beam ; upon the ends of the beam are fastened the movable frames which support the pans. There is a simple method of arresting the motion by moving the lever, and the delicacy of the balance is increased by placing a weight upon the index, whereby the centre of gravity is elevated. Knife-edges are done away with entirely.

How may Balances be protected ? By enclosing them in glass cases with convenient sliding doors.

How are liquids measured ? In graduated vessels; vessels of tinned copper, tinned iron, and enameled sheet iron, called agate, are usually employed for quantities larger than one pint; but glass measures are preferable for quantities of one pint or less. The former are generally made larger at the bottom than at the top; the latter are either conical, with apex at the bottom, or cylindrical, and graduated on the sides. It is better that the marking be on both sides of the graduate.

How would you test a glass graduate ? Place it upon a perfectly level surface, then pour into it 455.7 grains distilled water at 15.6° C. (60° F.). This should measure one fluidounce; or, measure into the graduate 30 C.c. of water (29.57 C.c.) for a fluidounce.

What is a graduated Pipette ? A glass tube graduated on the side, with a constricted point. It is used by applying suction to the upper end, and holding the liquid in the tube by placing the finger on the upper end while reading off the contents.

What is a Meniscus, and for what is it used ? Owing to capillary attraction, the top of the liquid in a graduated pipette presents a cup shape. This is called a meniscus. A line drawn through the bottom of the meniscus is usually selected as the reading point.

What is the size of a drop ? Erroneously, a drop is supposed to be a minim ; but though this may be approximately true when applied to water, it is not true in regard to any other liquid. Thick, viscous liquids produce large drops ; heavy, mobile liquids small ones.

A drop of syrup of acacia is five times as large as a drop of chloroform. The shape and surface from which the drop is poured also influences its size.

SPECIFIC GRAVITY. What is Specific Gravity? The comparative weight of bodies of equal bulk. It is ascertained by weighing the bodies with an equal bulk of pure water at a given temperature and atmospheric pressure, which is taken as one.

How would you obtain the Specific Gravity of a body? To obMETROLOGY.

tain the specific gravity of a body, it is only necessary to balance it with an equal bulk of the standard, and ascertain how many times the weight of the standard is contained in its weight. Ex. A fluidounce of water (standard) weighs 455.7 grains ; a fluidounce of lime-water weighs 456.3 grains; 456.3 : 455.7 = 1.0015, that is, the lime-water weighs 1.0015 times more than water, bulk for bulk. In other words, its specific gravity is 1.0015. A fluidounce of alcohol weighs 422.8; 422.8 • 445.7 = 0.928, specific gravity.

What general rule may be given for finding Specific Gravity ? Divide the weight of the body by the weight of an equal bulk of water; the quotient will be the specific gravity.

What method is usually adopted to ascertain the weight of the equal bulk of water in taking the Specific Gravity of solids ? A solid body immersed in water will displace its own bulk; it is required to find out the weight of this equal bulk of water. This might be ascertained by immersing the body in a vessel of water already full, then saving and weighing the displaced water which runs over. But there is a better way of finding out. Archimedes filled his bath-tub too full of water, one day, and it overflowed when he got into it. This led him to experiment, and he found that when weighed in water he lost as much weight as the water he displaced weighed. It is only necessary, then, to weigh a body first in air, then in water, and note its loss of weight when weighed in the latter medium. This loss is evidently the weight of an equal bulk of water. By our rule, we divide the weight of the body by the weight of an equal bulk of water; and it follows that it is the same thing to say: divide the weight of the body by its loss of weight in water, for that loss is the weight of an equal bulk of water. The quotient will be the specific gravity.

How would you take the Specific Gravity of a body heavier than water ? Four methods are used. 1st method : Accurately weigh the substance and note the weight. Now suspend the body from the hook at the end of the scale-beam with a horse-hair, so it shall hang a little above the scale-pan; next, place a small wooden bench in such a manner that it shall straddle the scale-pan, but not touch it; place a small beaker on the bench, partly filled with water, in which submerge the suspended body, noting the loss of weight by the use of proper weights on the opposite scale-pan; after which apply the rule already given. Ex. Weight of a piece of copper in the air, 805.5 grains ; weight in water, 715.5 grains ; loss of weight, 90 grains. 805.5 = 90=8.95, sp. gr. 21. method : With the specific gravity bottle. Add 1000 to the weight of the substance in the air. Now drop it into a 1000-grain specific gravity bottle, fill the bottle with water and weigh again. Subtract the ad sum from the Ist sum, and the difference is the loss of weight in water. Now apply the rule. Ex. A piece of aluminum wire weighs 100 grains in the air. 100

+ 1003=1100. Dropped in a 1000-grain specific gravity bottle, and the bottle filled with water, the weight of both is 1062. Then 1100 — 1062 = 33 grains, the loss of weight in water. 100 = 38 = 2.63, specific gravity. 3d method : With the graduated tube. Drop the substance into a tube graduated so that each space shall indicate a grain or gramme of water, and note how much higher the liquid rises in the tube, which is the weight

of an equal bulk of the substance. This known, apply the rule. 4th method : By immersing the solid in a transparent liquid of the same density. Drop the solid in a liquid of sufficient density to float it, then reduce its density with water until the solid neither rises nor sinks, but swims indifferently. The specific gravity of the liquid and solid will now be the same. Take out the solid and find the specific gravity of the liquid with the specific gravity bottle.

How would you proceed if the solid were soluble in water ? Use oil or some other liquid in which the solid is not soluble, as though it were water, then, by the following proportion, find the loss of weight in water; as the specific gravity of oil is to the specific gravity of water, so is the loss of weight in oil to the loss of weight in water. Then apply the rule.

How would you take the Specific Gravity of a solid lighter than water ? Force the substance under water by attaching a heavier body to it. First weigh both in the air, then both in water, and the difference will be the loss of both in water. A simple subtraction will give the loss of weight of one. Then apply the rule.

With what apparatus would you take the Specific Gravity of a liquid ? A specific gravity bottle, hydrometer, or specific gravity beads.

How would you construct a Specific Gravity bottle ? A bottle with a long, slim neck is counterpoised by an appropriate weight, and distilled water at the appropriate temperature, 15° C. (60° F.) poured in until it contains 1000 grains. The height reached by the water in the neck is then scratched thereon with a file, and it is ready for use.

What are the Specific Gravity beads ? Little pear-shaped, hollow globes of glass, loaded at the apex, and arranged to float indifferently in liquids of the specific gravity for which they are gauged, but to sink or swim in liquids that are lighter or heavier than they are.

Give directions for using the Specific Gravity bottle for taking the Specific Gravity of Liquids. Counterpoise the bottle and fill it to the mark with the liquid to be examined. The number of grains the liquid weighs, properly pointed off decimally, is its specific gravity. A 1000-gr. specific gravity bottle will hold 1160 grains of hydrochloric acid. Point off decimally 1.160, which is the specific gravity of hydrochloric acid. A 1000-gr. specific gravity bottle will hold 750 grains of ether. Point off decimally 0.750, thus showing the relation to the specific gravity of water, I.

If a bottle of any size is substituted for the 1000-gr. bottle, what equation will give the specific gravity ? As the number of grains of water the bottle holds is to 1000 (the specific gravity of water), so is the number of grains of liquid it holds, to the specific gravity of the liquid.

Describe the Hydrometer. As now constructed, the hydrometer usually “ consists of a glass tube loaded at the bottom with mercury or small shot, having a bulb blown in it just above the loaded end." The principle of its action depends upon the fact that a solid body floating in a liquid displaces a volume of liquid exactly equal to its own weight.

Into what two general classes may Hydrometers be divided ? Ist, those for liquids heavier than water; 2d, those for liquids lighter than water. The first class are called by the French Pèse-Acide, or Pèse-Sirop, and the second class Pèse-Esprit.

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What other class of Hydrometers is in use? Those intended to sink, by the addition of weights, to a given mark on the stem, and thus displace a constant volume.

What is a Baumé Hydrometer? The instrument devised by Baumé is peculiar only in so far as its system of graduation is concerned. This was made in the following manner: ist, for liquids heavier than water, the instrument was loaded with sufficient mercury to sink it in water to a convenient point near the top, which was marked o. It was then placed in a 15 per cent. salt solution, and the point at which it rested marked 15; the interspace between o and 15 was now marked off into 15 equal spaces, and the scale below extended by marking off similar spaces. 2d, for liquids lighter than water, a 10 per cent. salt solution was used, and the instrument loaded to sink into it to a point just above the bulb, which was marked 0. It was then allowed to sink in water, and the point of rest marked 10. The interspace between o and 10 was now divided into 10 equal spaces, and the scale above extended by marking off equal spaces.

What is the objection to Baumé's Hydrometer ? The graduations are entirely arbitrary, necessitating computation to determine the corresponding specific gravity.

What Hydrometer is rapidly taking its place? The Specific Gravity Hydrometer; the graduations upon the stem indicating at once the specific gravity.

Urinometer, saccharometer, elæometer (for fixed oils), and alcoholometer, and hydrometers for the special purposes indicated by their names.

HEAT.
What is heat? Heat is molecular motion.
What is a Furnace ? A species of stove for generating heat.

What are the elements of a furnace ? The air-flue, combustionchamber, and vent or chimney.

What proportion should they bear to each other? The special object sought in constructing the furnace must determine the proportions these shall bear to each other.

What is the best fuel for generating heat ? Anthracite Coal.

How much air is required to burn one pound of coal? Theoretically, 150 cubic feet; practically, twice that.

What liquids are used for fuel in pharmacy, and on what does their heating power depend? Alcohol, petroleum or coal oil, and benzin or gasolene. They all contain C and H (alcohol, 34 per cent. O in addition), on which their heating depends. *

What is Illuminating Gas? A mixture of carburetted hydrogen (CH), which is its principal constituent, with considerable hydrocarbons, hydrogen, carbon dioxide and monoxide, aqueous vapors, and traces of oxygen and nitrogen.

How may it be fitted for heating purposes? By mixing it with air.

* For special apparatus for developing heat for pharmaceutical manipulations, see Remington's " Practice of Pharmacy."

This is done by admitting air below the flame, using special apparatus for

this purpose.

Describe a Bunsen Burner. A brass tube, four inches high, with four large circular holes near the base, to admit the air, which may be regulated by a perforated brass ring which surrounds the tube, is supported by a metal pedestal, and connected with a gas fixture by a tube. The coal-gas admitted mixes with the air, and burns at the top of the tube with an intensely hot, colorless flame.

How would you measure heat ? By the thermometer.

Describe a Thermometer. A thermometer consists of a glass tube with capillary bore sealed at one end, and the other end terminating in a bulb. The bulb is filled with mercury or other fluid, which, being expanded by heat, rises in the tube and indicates the degree of heat, either on an index scratched on the tube itself, or marked on a piece of paper against which the tube is placed.

Describe the three scales for marking thermometric degrees now in use.

The scales are, 1. Centigrade; 2. Fahrenheit, and 3. Réaumur. In the Centigrade scale, the freezing point of water is zero, the boiling point 100°, and the intervening space is divided into 100 equal parts called degrees. In the Fahrenheit scale, the freezing point of water is 32°, the boiling point 212°, and the intervening space is divided into 180 equal parts called degrees. In the Réaumur scale, the freezing point is zero, and the boiling point 80°.

What ratio do the three scales bear to each other, and how would you convert the scale of one into the other ? Ratio : 5:9:4.

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FORMULÆ FOR THE CONVERSION OF DEGREES OF ONE THERMO

METRIC SCALE INTO THOSE OF ANOTHER.-Attfield. F. = Fahrenheit. C. Centigrade. R. Réaumur. D. = Observed Degree. If above the freezing point of water If below freezing, but above 0° F. (32° F. ; 0°C.; 0° R.).

(17.77° C.; -14.22° R.). F. into C., (D 32) • 9 X 5 F. into C., .

D) + 9 X 5 F. R.,

19 X 4
F. R., --(32

X4
C. F.
D: x 9 + 32

C. F.

32

5 X 9) R. F., D: 4 X 9 + 32

R. F.,

32 If below o° F. (-17.77° C.; -- 14.22° R.). For all degrees, F. into C.,. :-(D + 32) = 9 X 5 C. into R.,

D + 5 X 4 F. R., . -(D + 32) • 9 X 4

R.

D = 4 X 5 C. F., -(D5 X 9) - 32 R. F., . :-(D • 4 X 9)

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RULES. 1. To convert Centigrade degrees into those of Fahrenheit above 32, multiply by 1.8 and add 32.

2. To convert Fahrenheit degrees above 32 into those of Centigrade, subtract 32 and divide by 1.8.Remington.

How would you select a thermometer ? Choose one made of glass, thick enough to be strong, but thin enough to be delicate, with graduations marked on tube, which should be of equal diameter throughout, with flat or elliptical, perfectly uniform bore. It should be free from air, which

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