T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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mometers should be graduated as total or partial immersion thermometers. For t h e ordinary everyday use of a thermometer i t seems t o be quite customary t o immerse i t a few inches i n t h e b a t h or medium, t h e temperature of which is t o be measured. It also seems t o be quite customary t o neglect t h e stein correction. If these are t h e usual conditions of use i t will be seen t h a t more accurate results would Be obtained by using partial immersion thermometers, a n d about as accurate results would be obtained by such usage as would be obtained with t o t a l immersion thermometers, even when t h e stem correction was applied, unless d u e care were t a k e n t o determine t h e stem correction with szcficient accuracy.
Vol. 13, No. 3
LABORATORY THERMOMETERS By W. D. Collins1 WASHINGTON, D. C. Received January 10, 1921
I n t h e following discussion "thermometer" means t h e usual mercury-in-glass thermometer with engraved stem. T h e t y p e with enclosed glass scale is much superior for m a n y operations, but in t h e ranges regularly used is not yet produced sufficiently generally in t h e United States t o make possible its adoption as stock apparatus. T h e mercury thermometer a t its best is not a n in: s t r u m e n t of extreme precision. At its worst i t m a y be very misleading. T h e large errors which are occasionally found are due t o carelessness in manufacture, CONCLUSIONS T h e above considerations m a y be summarized i n usually in t h e process of pointing. Excessive deprest h e statement t h a t in all cases where t h e application sion of t h e zero point after heating t o a high t e m of stem corrections is neglected, which includes a v a s t perature does not occur unless t h e maker has failed majority of ordinary routine laboratory temperature t o use proper glass for t h e bulb. Irregularities in t h e bore rarely have a n y serious effect on t h e accuracy measurements, more accurate temperature measurements would be attained by t h e use of thermometers if t h e distances between reference points are not too, great. If reasonable care in annealing or aging h a s graduated as partial immersion thermometers; t h e been exercised t h e readings d o not change much with same statement would apply for measurements a t t h e time. Slight errors due t o all these causes will be higher temperatures (above 200" C. or thereabouts), even if stem corrections a r e applied, when t h e ordinary found in any thermometer a n d cannot be allowed for method of estimating average stem temperature is with great precision. On t h e other hand, a well-made, carefully pointed thermometer is a s accurate a n d used instead of t h e more accurate capillary thermomreliable as m a n y of t h e other features of regular chemeter method. At t h e lower temperatures, on t h e other hand, a slight advantage rests with t h e t o t a l ical work in which it is used. T h e discussion by Waidner and Mueller in t h e preimmersion thermometer, if t h e stem correction is deceding article covers t h e question of t h e accuracy of termined a n d applied in t h e usual manner, i. e . , by thermometers made t o be used with total immersion t h e intelligent use of a n auxiliary thermometer t o determine t h e average stem temperature. T h e r m o m - or partial immersion. It is well known t h a t a l a r g e eters graduated i n intervals smaller t h a n 0.5' C. proportion of t h e temperature measurements in regular should n o t , in general, be graduated as partial immer- chemical laboratory work are made with a greater or sion thermometers, if t h e accuracy of which they a r e less length of emergent mercury column without corcapable is desired, unless such finer graduation be rection. It has been objected t h a t errors may result from deemed of sufficient importance solely from t h e s t a n d introduction of partial immersion thermometers i n t o point of convenience in reading. laboratories where those pointed for total immersion have been in use. It does not seem likely t h a t anyone The Albany Chemical Company has been ordered by Federal careful enough t o correct for t h e emergent stem on a Judge Dietrich to withdraw all applications for a trade-mark total immersion thermometer would fail t o use propof the word "aspirin." The Company was cited by the Federal erly one marked for partial immersion. T h e others Trade Commission in complaint of unfair competition, being would all gain in accuracy. charged with falsely advertising that no other person or corporaT h e specifications given below were prepared by tion has a right to the use of the word "aspirin." Upon expiraMr. E. F. h4ueller of t h e Bureau of Standards t o tion of the patent on the word, it became a descriptive name and not the property of anyone. include certain features which had been suggested by various members of t h e Committee on Guaranteed The Jounral of Commerce reports that by the amalgamation Reagents a n d S t a n d a r d Apparatus, a n d had been of Aniline Dyes 81 Chemicals, Inc., with the Swiss Society for discussed at a conference of members of t h e committee Chemical Industry, an amalgamation of the three Swiss firms, with Dr. Waidner a n d Mr. Mueller. I t was felt t h a t the Geigy Co., Ltd., The Chemical Works (formerly Sandoz), t h e three thermometers described furnish a good worliand the Society for Chemical Industry, with the two American ing set for general laboratory use. firms of Ault & Wiborg and Aniline Dyes & Chemicals, is acT h e thermometer with a range from -20" t o 150" complished, since the recent sale of Ault & Wiborg to the Geigy C. in single degrees is much more useful t h a n one with Company was really a sale to the Swiss amalgamation. t h e widely used range from -10" or -5" t o 100" or 110" C., a n d t h e cost need not be much greater. T h e A car containing 49,494 lbs. of sodium peroxide manufactured by the Niagara Electro-Chemical Company, a t Niagara length of t h e degree divisions is better t h a n on a 0" Palls, N. Y., recently exploded while standing on the tracks in t o 100" thermometer of t h e same length for subdivithe freight yard. No reason for the disaster has been an1 Chairman, Committee on Guaranteed Reagents and Standard Ap-nounced. paratus, American Chemical Society. ~
M a r . , 1921
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E X I S T R Y
sion b y t h e eye by those without special practice i n such reading. T h e -10" t o 360" thermometer covers a s nearly as seems practicable t h e whole range of temperatures measured i n regular chemical laboratory work. It was felt t h a t t h e danger of breakage i n handling a n d use would be increased more t h a n proportionally b y additional length, while a shorter thermometer with this range would h a v e t h e degree divisions t o o small F o r t h e sake of added strength t h e diameter limits h a v e been raised from those for t h e 150" thermometer. Thermometer 3 has been added t o provide for t h e more accurate measurement of temperature u p t o 100 '. As explained b y Waidner a n d Mueller, t h e graduation i n 0.2" divisions makes it o u t of t h e question t o point a n d use this a s a partial immersion thermometer. T h e uncertainty of t h e reading m a y a m o u n t t o one or t w o divisions, making t h e recording of fractions of divisions absurd. Despite t h e greater length, t h e diameter has been specified smaller t h a n t h e 360" thermometer, because it will probably be used more carefully, a n d it is felt t h a t a small diameter is a n advantage except for strength. T h e specifications call for accuracy which should be obtainable without excessive cost. If much greater accuracy is desired i t is better obtained b y careful compai-ison with standard thermometers a n d t h e use of t h e corrections so determined, rather t h a n b y a t tempting t o secure a thermometer which can be used without correction for t h e more exacting work. Tests a n d certificates of corrections for thermometers can b e secured from t h e Bureau of Standards, b u t t h e expense a n d time required are justified for only a small proportion of thermometers used i n chemical work. A laboratory m a y d o very well, especially with partial immersion thermometers, b y having one or t w o of each range tested a t t h e Bureau of Standards a n d comparing all others with them. Serious errors can be detected easily i n a n y laboratory without such standardized thermometers. T h e zero point can be tested b y placing t h e thermometer u p t o t h e immersion point or t o t h e t o p of t h e mercury in melting finely cracked ice, keeping t h e thermometer wet witho u t an excess of water. T h e 100" point can be tested b y placing t h e thermometer u p t o t h e immersion point i n steam, applying a n y necessary correction for departure of atmospheric pressure from 760 mm. Mr. R. hI. Wilhelm h a s suggested' t h e use of naphthalene a n d anthracene for checking t h e points 218" and 340", respectively. H e states t h a t t h e boiling points increase 0.05' a n d 0.07", respectively, per m m . of mercury increase i n pressure. T h e requirements in t h e General Supply Committee Schedule for purchases b y t h e government laboratories in Washington during t h e fiscal year 1922 are based o n t h e specifications given below. If other laboratories use these specifications there should be a concentration of production o n these items which will bring down t h e price and improve t h e quality of thermometers for chemical laboratory work. 1 "Emergent Stem Correction for Thermometers in Creosote Oil Distillation Flasks," U. S. Bureau of Standards, Technologzc Paper, 49 (1915), 16.
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SPECIFICATION No. 1 Thermometer: -20" to 150" C. in 1" intervals; 8 cm. immersion. Total length 30 to 31 cm. (approximately 12 in.); diameter of stem 5.5 t o 6.5 mm. Bulb, cylindrical; not larger than stem and not over 2 cm. long. Bulb and stem to be of suitable thermometric glass;
enamel-backed thermometer tubing ; diameter of capillary must be a t least 0.1 mm. Thermometer to be graduated for 8 cm. immersion, a mark being etched on the stem 8 cm. above the lower end of the graduabulb to indicate this depth of immersion. The -20' tion must be above the 8 cm. mark. The length of the graduated to +150" must be a t least 15 cm. If above scale from -20' specifications are complied with, it is permissible to continue or above 150". Every fifth line, begraduations below -20' ginning a t -20 ', to be longer than the intermediate lines; numbering a t 10" intervals; error a t any point not to exceed 1". The space above the mercury may be evacuated or gas-filled. The reservoir a t the top of the capillary shall be large enough to permit heating of the thermometer to 200" C. without danger of breakage due to the heating. The thermometer shall be marked "8 cm. immersion," and shall also be marked with the manufacturer's name or trade-mark and a serial identification number. The thermometer shall be made with a small glass ring or loop a t the top. Suitable material and good workmanship shall be employed throughout t o produce a usable thermometer. The thermometer is t o be supplied in a suitable case. SPECIFICATION No. 2 Thermometer: -10" t o 360" C. in I" intervals; 8 cm. immersion. Total length 37 to 38 cm. (approximately 15 in.); diameter of stem 6 to 7 mm. Bulb, cylindrical; not larger than stem and not over 2 cm. long; bulb and stem t o be of suitable thermometric glass; enamelbacked thermometer tubing; diameter of capillary must be a t least 0.1 mm. Thermometer t o be graduated for 8 cm. immersion, a mark being etched on the stem 8 cm. above the lower end of the bulb to indicate this depth of immersion. The length of the graduated scale from -10" to +360° must be a t least 26 cm. If above specifications are complied with, it is permissible to continue graduations below -10' or above 360". It will be necessary to allow a portion of the scale to e x t y d below the 8 cm. mark. Every fifth line, beginning a t -10 , t o be longer than the intermediate lines; numbering a t 10' intervals. The thermometer must be suitably annealed; error at any point up to 150" not to exceed 1'; a t higher p$nts, up to 300", not to exceed 1.5":above 300°, not to exceed 2 . The spaces above the mercury must be filled with a dry inert gas a t a pressure sufficient to prevent separation of the column a t any temperature of the scale. The volume of the space above the 360' graduation must be large enough to permit heating the thermometer to 400 " C. without danger of breakage due to the heating. The thermometer shall be marked "8 cm. immersion," and shall also be marked with the manufacturer's name or trademark and a serial identification number. Suitable material and good workmanship shall be employed throughout to produce a usable thermometer. The thermometer is to be supplied in a suitable case. SPECIFICATION No. 3 Thermometer: -5' to 105" C. in 0.2" intervals. Total immersion. Total length 45 to 46 cm. (approximately 18 in.); diameter of stem 5.7 to 6.7 mm. Bulb, cylindrical, not larger than stem and not over 3 cm. long; bulb and stem to be of suitable thermometric glass; enamelbacked thermometer tubing; diameter of capillary must be a t least 0.1 mm. The length of the graduated scale from -5' to +105" must be a t least 33 cm. If above specifications are complied with, it is permissible to continue graduations below -5" or above 105". Each degree mark is to be longer than the intermediate marks; numbering $t 2" intervals. The error at any point must not exceed 0.3 . The space above the mercury may be evacuated or filled with dry inert gas. The reservoir at the top of the capillary shall be large enough to permit heating of the thermometer to 140" C. without danger of breakage due to the heating. The thermometer shall be marked with the manufacturer's name or trade-mark and a serial identification number. The thermometer shall be made with a small glass ring or loop at the top. Suitable material and good workmanship shall be employed throughout to produce a usable thermometer. The thermometer hall be supplied in a suitable case.
