quickly. A cheaper thermometer, which will answer for many purposes, has a paper scale inside of a glass tube (see Fig. 80). These should not be used for temperatures over 300° F., as in time the paper becomes charred. It is a good practice to send a thermometer to be officially tested,' and then to reserve it as a standard for correcting ordinary instruments. As glass usually reaches its limit of contraction in three years, such a thermometer should be at least this old before it is sent. Table of Melting-Points of Official Substances. 1 Thermometers are examined, and certificates are issued showing the corrections, by Winchester Observatory of Yale College, New Haven, Conn. According to the dynamical theory, how is heat produced? What is the objection to using wood as a source of heat in pharmaceutical operations? Is charcoal more or less convenient, and why? What advantage has anthracite coal? What is the objection to bituminous coal? How is water heated in an ordinary range? What liquids are used for heating purposes in pharmaceutical operations? What objection is there to the use of alcohol? What is the arrangement of the so-called Russian blast-lamp? How may benzin or gasolin be burned without danger from explosion? Is kerosene or coal oil safer than gasolin? If so, why? facture? flame. Does coal oil require a wick to burn satisfactorily? What is the disadvantage of using a wick? Of what does ordinary illuminating gas consist? How is it produced? Give an explanation of the three zones that are apparent in an ordinary gas How may ordinary gas be burned so as to become a source of heat rather than of light? What is a Bunsen burner? What is the objection to the ordinary Bunsen burner? How may this be obviated? How does the length of the perpendicular tube affect the smokeless character of the flame? Describe Fletcher's radial burner. What are the chief points to be secured in a good gas stove? Describe the Economy furnace. What are the chief advantages in this stove? What are the advantages of the use of illuminating gas as a source of heat? In pharmaceutical operations, how are degrees of temperature measured? What three scales of degrees of heat for thermometers are used? Which is most largely used in this country? Which is used in the U. S. Pharmacopoeia? What are the freezing- and boiling-points of Fahrenheit's scale? How is the intervening space divided? What are the freezing- and boiling-points of the Centigrade scale? How is the intervening space divided? What are the freezing- and boiling-points of Réaumur's scale? How is the intervening space divided? How may Centigrade degrees be converted into those of Fahrenheit above 32? CHAPTER III. USES OF HEAT. THE consideration of the uses of heat in pharmacy will follow naturally the preceding chapter upon its generation and measurement, and the subject may be properly treated of under two classes,-viz.: 1, those operations in which comparatively high temperatures are required, and, 2, those which require moderate or low temperatures. It will be readily noticed that the latter class will embrace nearly all of the more important pharmaceutical operations in which heat is employed. Operations in which comparatively High Temperatures are required. In this class of operations must be placed some which seem to be in danger of becoming lost arts through the growth of special methods, which are now conducted on a large scale by manufacturers, who supply the products of their skill so cheaply that the homemade apparatus is often produced at a pecuniary loss. It will, nevertheless, be found useful to refer briefly to these operations, for a certain amount of knowledge will frequently be of service to the practical worker in emergencies and on special occasions. The Use of the Blow-Pipe.-A blow-pipe in its simplest form is a metallic tube, usually of brass or copper, slightly conical, gradually tapering to a minute orifice, the narrowest portion being curved so that the axis of the orifice is at right angles to that of the principal portion of the tube. It is used by placing the widest end in the mouth, and inserting the other end into the edge of the flame, and forcing a current of air through the tube, with the effect of increasing the intensity of the flame by converting it into a miniature blast. Some skill and practice are required to produce an unremitting current of air, and this is effected by keeping the muscles of the cheeks distended and constantly supplying air from the lungs as it is needed. When the blow-pipe is used with a luminous flame, the interior of the flame, owing to the carbon not being wholly oxidized, has the power of deoxidizing or reducing oxides, whilst the outer flame has opposite or oxidizing properties: a piece of lead glass tube held in the inner flame will be blackened through the reduction of the lead oxide to the metallic state; if this stain is held in the outer flame the metal is reoxidized, dissolves in the glass, and the glass again becomes transparent. The blow-pipe is useful in pharmacy in working and bending glass, in testing fusible chemical substances, in soldering apparatus, etc. The various forms of blow-pipes in common use are shown in Figs. 86 to 91. The Fletcher's gas blow-pipe, shown in Fig. 92, furnishes an excellent and very powerful blast which is capable of delicate adjustment. It has a universal ball-and-socket joint, which enables it to be used in any position. The very convenient foot-bellows, shown in Fig. 93, may be used in connection with it for producing the blast. The sides of this FIG. 86. FIG. 87. FIG. 88. FIG. 89. FIG. 90. FIG. 91. Plain blow-pipe. Bulb. Black's. Berzelius's. Plattner's. Plattner's (dissected). bellows are of stout leather, and the reservoir of air beneath is obtained by stretching and fastening a circular piece of thin rubber cloth over the FIG. 92. lower orifice and preventing too great expansion and rupture by enclosing it in a net: this form, with the reservoir below, is preferable to that formerly in use, which had the rubber cloth above; the advantages are greater protection against injury from falling Gas blow-pipe. Foot-bellows. articles, and less obstruction to the valves through sucking in dust from the floor. Crucible Operations.-A crucible is a cup-shaped vessel made of platinum, silver, black lead, iron, porcelain, wedgwood-ware, or clay, and intended to withstand a very powerful heat. It is used for fusing metals or heating metallic oxides or organic substances, and is very useful in chemical analysis. The Hessian crucible (see Fig. 94) is the cheapest it is unfitted for delicate operations, for, although capable of withstanding great heat, its porous character permits the ready absorption of many substances. The black-lead crucible is more expen |