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scale for measuring the rise and fall of the liquid within the tube; mercury is preferred for all temperatures not below —40° C. (at which point it freezes), on account of its pon-adhesion to the sides of the glass tube, and consequent convex surface, and its great sensitiveness to even the slightest change in temperature. Absolute alcohol, although admirably adapted to very low temperatures, cannot be used for measuring heat intensity above 78.3° C., its boiling-point. The space above the liquid in the tube is deprived of air, so as to insure the ready and juniform rise of the liquid when expanded by heat.
As all glass vessels continue to contract for some years after they have been made, absolutely correct measurement of temperatures can only be obtained if the error of the thermometer is known ; such error can easily be ascertained by two very simple experiments. Immerse the bulb of the thermometer in crushed ice for fifteen or twenty minutes, and note the point on the graduated scale to which the mercury will sink; after five minutes more of immersion, again examine to see whether the mercury has remained stationary; if the mercury receded to 0° C. (32° F.) and remained at this point, the thermometer is correct as far as the freezing-point is concerned. To test its accuracy at higher temperatures, suspend the thermometer in steam rising from pure boiling water, in such a manner that it is completely surrounded by it, for the unconfined vapor of a boiling liquid has the same temperature as the boiling liquid itself; after thirty minutes, note the point to which the mercury has risen and continue the heat for ten or fifteen minutes, and examine again; if the mercury has risen to 100° C. (212° F.) and remained at that point for ten or fifteen minutes, the thermometer may be considered correct as compared with the boiling-point of water. Clinical thermometers, used by physicians for taking the temperature of fever patients, should be supplied with a certificate showing
their error, as this in some cases may amount to nearly } degree. Since 1880 the Winchester Observatory at Yale College, New Haven, Conn., has had in operation a special bureau for the examination of thermometers; as glass tubing will continue to contract for three or four years, clinical thermometers should have been “seasoned” for at least that time before they are examined, so that any error found may remain constant.
During the past two years, thermometers of great accuracy, intended for very high temperatures, up to 550° C. (1022° F.), have been made in Germany, of special glass, known as “Jepa resistance glass,” which is very hard and non-contractile. In order to prevent boiling of the mercury, which ordinarily occurs at about 357° C. (674.6° F.), the capillary tube is expanded at the upper end and filled above the mercurial column with compressed dry carbon dioxide. Still more recently (1891) thermometers have been manufactured in which the indicator consists of an alloy of sodium and potassium, instead of mercury, and which may be used for temperatures running as high as 650° C. (1202° F.). The alloy is enclosed, as in the previous case, in “resistance” glass, and the space above the alloy is filled with nitrogen at such pressure that, when the bulb becomes red-hot, the pressure inside is equal to that of the atmosphere. The glass of the bulb is attacked by the alloy and turned brown, but this occurs at the time of filling, and the coating then formed upon the surface of the glass protects it from further action.
For registering still higher temperatures, instruments known as pyrometers are employed, which are, however, not very trustworthy; they are of two kinds, Wedgewood's pyrometer, based on the contraction of clay, and Broguiart's pyrometer, based on the expansion of metals. When it is desirable to note the highest or lowest temperature reached during any fixed time, maximum and minimum thermometers, so constructed that a small metallic or glass indicator is carried to the highest or lowest point reached by the mercury or alcohol, and left at that point when the volume again changes, are used.
Three different thermometric registers, known as the Fahrenheit, Celsius or Centigrade, and Réaumur scales, are in use. For scientific purposes the Centigrade scale is now universally employed, while the Fabrenheit scale is in common use in this country and Great Britain, and the Réaumur scale is ordinarily used in Continental Europe. The graduations of all three scales are arbitrary, yet based upon careful observations of the respective authors. Fahrenheit, a German, who invented the mercurial thermometer, in 1709, observed that a quantity of mercury immersed in a mixture of ice and salt (considered by him as the absolute zero of temperature) amounted to 11,124 volume parts, and when immersed in melting ice expanded to 11,156 volume parts, showing an increase of 32; the same quantity of mercury immersed in boiling water expanded to 11,336 volume parts, or an increase of 212.
These observations led Fahrenheit to mark the freezing and boiling points of water at 32 and 212 degrees above zero respectively, and to divide the space between these two points into 180 equal parts. Réaumur, a Frenchman, found that 1000 volume parts of alcohol of a given strength increased to 1080 volume parts between the freezing and boiling points of water, and he marked these two extremes as 0 and 80 respectively, dividing the intervening space into 80 equal parts. Celsius, a Swede, adopted the more convenient plan of centesimal division, and fixed the freezing and boiling points of
pure water at 0 and 100 respectively; his scale is generally termed the Centigrade scale and is preferred for scientific work.
When writing temperatures on the different scales, it is customary to use the abbreviations F. or Fahr. for Fahrenheit, C., Cent, or Cels. for Celsius, and R. or Réaum. for Réaumur, as, 32° F., 100° C., and 80° R. On all the scales, the degrees are divided into plus and minus degrees, as they may be above or below the zero point; the latter being always distinguished by the prefix of the — sign, and whenever this sign is wanting, the degrees of heat being understood to be above
zero ; thus 18° F. would indicate 18 degrees above 0, although 14 degrees below the freezing-point, etc.
Fig. 74 illustrates the relative graduations on the respective thermometric scales.
As equal spaces on the Centigrade and Fahrenheit scales are divided into 100 and 180 degrees respectively, it follows that each degree on the former scale is equal to 1.8 degrees on the latter, and since 80 degrees on the Réaumur scale equal 180 degrees on the Fahrenheit scale, every degree of the former must correspond to 2.25 degrees of
Section of Zincke's thermometer.
Réaumur, Centigrade, and Fahrenheit
the latter. Every Réaumur degree is equal to 1.25 Centigrade degrees. The following rules for the conversion of thermometric values are useful.
To convert Centigrade into Fahrenheit : Multiply by 1.8 and add
32; for any number of degrees above or below the freezing-point on the Centigrade scale when multiplied by 1.8 yield the corresponding number of degrees above or below the freezing-point on the Fahrenheit scale.
To convert Fahrenheit into Centigrade : Subtract 32 and divide by 1.8; for any number of degrees above or below the freezing-point on the Fahrenheit scale when divided by 1.8 yield the corresponding number of degrees above or below the freezing-point on the Centigrade scale.
To convert Réaumur into Fahrenheit, or Fahrenheit into Réaumur, substitute 2.25 for 1.8 in the preceding rules.
To convert Centigrade into Réaumur, divide by 1.25; and to convert Réaumur into Centigrade, multiply by 1.25.
Examples : Convert 25° C. into F. ; 25 X 1.8=45 and 45 +32 = 77. Answer, 77° F.
Convert -15° C. into F.; --15 X 1.8= -27 and -27 +32= 5. Answer, 5° F.
Convert – 40° C. into F.; -40 X 1.8= -72 and — 72 +32= -40. Answer, -40° F.
Convert 60° F. into C.; 60 – 32= 28 and 28 = 1.8=15.55+. Answer, 15.55+ ° C.
Convert 18° F. into C.; 18 -32=-14 and 14:1.8= -7.77+Answer, —7.77 +° C.
Convert -12.5° F. into C.; -12.5 - 32=-44.5 and -44.5 • 1.8= –24.72+. Answer, —24.72+° C.
Convert 30° R. into F.; 30 X 2.25= 67.5 and 67.5 + 32=99.5. Answer, 99.5° F.
Convert -5° R. into F.; -5 X 2.25=-11.25 and -11.25 + 32=20.75. Answer, 20.75° F.
Convert 50° F. into R.; 50 - 32 =18 and 18= 2.25 = 8. Answer, 8° R.
Convert 4° F. into R.; 4-32=-28 and -28 -- 2.25 = --12.4. Answer, -12.4° R.
Convert 60° C. into R. ; 60 = 1.25=48. Answer, 48° R. Convert -8° C. into R.; -8 -1.25=-6.4. Answer, -6.4°R. Convert 28° R. into C.; 28 X 1.25=35. Answer, 35° C.
Convert -7.5° R. into C.; -7.5 X 1.25= -9.37 +. Answer, -9.37 +°C.
In order to avoid the use of the ordinary long thermometer for temperatures above 100° C., which might frequently prove annoying and give rise to inaccuracies in scientific work, special short thermometers have been devised, so constructed that the graduations of the scale begin a little below the boiling-point of water. (See Fig. 75.) These instruments, known as Zincke's thermometers, are from 4 to 6 inches in length, very accurately made, and are admirably adapted for testing the melting or boiling-point of substances at temperatures above 100° C.
COLLECTION AND PRESERVATION OF CRUDE DRUGS.
ALTHOUGH the collection and preparation of vegetable drugs is not in the hands of the pharmacist, but is carried on, often in a small way, by special drug-gatherers and collectors, it is thought fit to refer to the subject here.
The various parts of plants used in medicine cannot be gathered indifferently at all seasons of the year, since the peculiar juices of the plant in which its activity resides are more abundant in some parts than others at certain periods of the plant's growth. Roots of annual plants should be gathered immediately before the time of flowering; those of biennials, either late in the fall of the first year, or early in the spring of the second year, after the first appearance of the plant above ground; perennial roots should not be gathered until after two or three years' growth, and, in some cases, even four or five years are allowed for full maturity. Fleshy roots must be sliced, either transversely or longitudinally, previous to drying, in order to expose a larger surface to the air; whilst smaller and fibrous roots do not require this treatment. When artificial beat is to be used in drying roots, a temperature of 50° to 55° C. (about 122° to 131°F.) will be found sufficient, except in the case of a few succulent roots, where the temperature may be raised to 65.5° C. (150° F.).
Barks of trees should be gathered in the spring, but those of shrubs in the autumn, for at these seasons they are most readily separated from the wood. Only the inner bark being employed, the outer epidermis should be removed.
Leaves begin to lose their activity after the flowers appear, for the juices of the plant then go toward nourishing the latter; they should therefore be collected when fully developed, before they begin to wither. Leaves of biennials must be collected during the second season.
Herbs are generally understood to mean the whole plant, although the root is frequently rejected; they should be gathered when in flotver. If the flowers are not to be used with the stem, the latter should be collected before the flowers appear, but after foliation.
Flowers are preferably gathered before they are perfectly developed (expanded), since odor and color are then more pronounced ; the red or French rose offers a striking example. They should be collected in the morning, after the dew has disappeared, and be dried, without artificial heat, in the shade.