Bunsen burners are more frequently used in simple operations than other form (see Fig. 67). The coal-gas issues from a small orifice, O, near the base, passes up through a brass tube, H, four inches high, and is ignited at the top of this tube; four large circular openings surround the small orifice at the base, and these may be closed either wholly or in part by a perforated brass ring, R; this permits the regulation of the supply of air, which mixes with the gas as it ascends the tube, and a blue, smokeless, intensely hot flame may be produced; if the perforated ring is turned so that the air-openings are closed, a luminous, smoky flame results. One of the objections to the ordinary Bunsen burner is that, after being used for a time under a low gas-pressure, when the tube becomes hot the flame will sometimes recede and the gas become ignited at the lower orifice: this may usually be avoided by gradually turning the brass perforated ring, so as to admit less air to suit the diminished pressure. Prof. Morton corrects this receding of the flame by contracting the orifice of escape at the top to about two-thirds of the area of the tube see Fig. 68). That the length of the

FIG. 68.

Bunsen burner (Morton's).

Short burner.

Short burner, with support.

perpendicular tube does not materially affect the smokeless character of the flame may be proved by the use of the convenient little burners shown in Figs. 69 and 70. These are made by the Buffalo Dental Manufacturing Company, and have

proved very useful at the prescription counter. Bunsen burners with the tube arranged horizontally have

FIG. 71.

FIG. 72.

grown in favor because they are less likely to be overturned, and if they have a broad base they will easily support a large vessel. Fletcher's

FIG. 73.

radial burner (see Fig. 71) has the merit of having no loose parts, and, as the casting is well annealed, it is well adapted for rough usage, the gas issuing from narrow slits cut radially in the raised circular burner; the flame is solid and non-luminous: no gauze is needed to distribute the heat. In Fig. 72 is shown a very compact and useful gas-burner, well adapted for the dispensing counter, made by Bullock & Crenshaw; it is of the horizontal Bunsen type, and is furnished with an attachment for distributing the flame, and three short legs for supporting the vessel that is to be heated.

In many localities outside of cities and towns, gas made by vaporizing gasolin and mixing air with it is used for illuminating purposes. It is made by gas machines, as they are termed, the air-pump, operated by weights and pulleys or by a water-wheel, being usually located in the cellar of the residence or building, whilst the gasometer is buried underground at a safe distance. This gas is very satisfactory, but it has been only within a few years that it has been utilized for heating purposes. Special burners are required when this gas is used as an illuminant, and they require some adjustment at first to secure the proper proportion of air. Fig. 73 shows the Springfield laboratory burner, which gives a very hot, blue flame with this kind of gas, and it may also be used with ordinary gas. The milled head at the base of the burner is used to control the quantity of the gas passing through, whilst by revolving the burner itself upon the thread of the screw by which it is connected with the base the quality of the gas is determined,-i.e., the proper proportion of air is admitted.

Gas stoves are now made in such variety that it seems difficult to make a judicious selection for general pharmaceutical work: the error most frequently made is in the choice of those which are intended to produce only

FIG. 74.

Springfield labora

FIG. 75.

tory burner.

HOT WATER

Water-heater.

very high temperatures. It is very seldom that a heat of great intensity is desired in pharmaceutical operations. The chief points to be secured

in a good gas stove are-1, a smokeless flame; 2, a strong, firm, indestructible frame that will easily support a large or small vessel and is not easily overturned; 3, an easy and quick adjustment, whereby either a strong, well-sustained heat or a low, diffused heat may be obtained. Prof. Parrish devised a pharmaceutical stove which had these qualifications, but it is not made at present. Fig. 74 shows the gas stove known

in commerce as the Economy furnace. It is made by the American Meter Company, and of all of the gas stoves that have been used by the author, this is the one which is in every way most suited for pharmaceutical operations. It has a broad, low, strong base, and cannot be easily overturned, and a double ring burner, so arranged that either the small ring or both the small and large rings may be used. As it is only about four inches high, when placed upon the laboratory counter a vessel which is upon it and being heated is not elevated so that it cannot be conveniently stirred. It is nine inches square, and its consumption of gas when both rings are lighted is ten feet per hour.

One of the greatest conveniences that a pharmacist can have at a dispensing counter, where a large supply of hot water cannot be had from a boiler, is the water-heater shown in Fig. 75. If hot water is desired, the pipe at the top is connected with a hydrant, the water turned on, and the gas-burner lighted below; in a few seconds warm water, and in a minute or two hot water, will run from the lower pipe. Fig. 76 shows a convenient hot-water generator, well adapted for furnishing a supply of hot water in pharmacies which have not access to the water back of a range, but can use gas. It is shown in the illustration attached to an ordinary circulating boiler, and it can be depended upon to furnish a large quantity of warm water. It is made by the American Meter Company.

The advantages of the use of illuminating gas as a source of heat may be summed up as follows: 1. It may be made to furnish a clean, smokeless flame. 2. It is cheap when compared with alcohol and other sources of heat, and is particularly economical in large cities. 3. The supply is unremitting, and the inconvenience of continually supplying fuel, which is always present in other forms of stoves, is not experienced here. 4. The supply is under almost perfect control, and, after once regulating the flow suitable for a continuous operation, little appre hension need be felt, during the operator's enforced absence, of an injurious rise or fall in the temperature.

METHODS OF MEASURING HEAT.

To measure degrees of temperature in pharmaceutical operations thermometers are used exclusively. A thermometer may be described as an instrument consisting of a glass tube having a capillary bore, with a cylindrical or globular bulb blown at the end, the bulb and a part of the stem containing a liquid (usually mercury), and the tube being mounted upon a graduated scale, or the tube itself graduated, in order to measure the degree of expansion of the liquid when subjected to the influence of heat. Unfortunately, the value of the degrees of thermometers in common use is not the same, there being no less than three arbitrary scales,-Centigrade, Fahrenheit, and Réaumur, the latter rarely used.

The Centigrade, or Celsius's, scale is best adapted for scientific work; it is given the first place in the U.S. Pharmacopoeia, 1890. The freezingpoint of water is zero, 0°, and the boiling-point is 100°; the intervening space is divided into one hundred equal parts (see Fig. 78).

The Fahrenheit scale is much the most largely used in this country and Great Britain, and until the 1880 revision of the U. S. Pharmacopoeia it was used exclusively in pharmacy. The Centigrade degrees in the Pharmacopoeia are followed by those of Fahrenheit enclosed in parentheses, as 100° C. (212° F.). In Fahrenheit's thermometer the freezingpoint is 32°, and the boiling-point is 212°, the intervening space being divided into one hundred and eighty equal parts (see Fig. 79). In Réaumur's thermometer the freezing-point is 0°, and the boilingpoint is 80°.

In Figs. 81, 82, and 83 the three thermometers are shown together to facilitate comparison: the lowest figures indicate the freezing-points of each, the highest the boiling-points.

Rules.

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

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

Choice of Thermometers.-It is important that the pracFIG. 78. tical pharmacist should possess a good thermometer. The best form is one in which the graduations are made on the surface of the tube. The diameter of the instrument should be the same throughout its entire length; this permits its convenient use through perforated corks in distillations and other opera

8 8 8 8 8 8

CENTIGRADE

50

40

20

μο

00

tions where it is necessary to observe temperature, FIG. 79. and it is not so easily broken (see Fig. 79). The thickness of the glass of the bulb is not a matter of indifference: if too thick, the thermometer will not respond quickly to changes of temperature, whilst if too thin, the risk of fracture is very great. The bore of the tube should be flat or elliptical, and perfectly uniform throughout. The absence of air in the tube may be known by the descent of the mercury to the lowest part of the tube when the

5

O

Ω

Centigrade Fahrenheit Paper-scale thermometer. thermometer. thermometer.

Fahrenheit thermometer.

Centigrade thermometer.

Réaumur thermometer.

thermometer is inverted. A strip of opaque, white enamelled glass behind the bore of the tube is of great assistance in reading the indication