T H E J O U R S A L O F I J D C S T R I A L ALVD EXGILVEERING C H E M I S T R Y
M a r . , 1914
237
ture. Let tl be t h e t i m e of transpiration from left t o right a n d fz t h e corresponding time from right t o left. Let P o be t h e pressure, corrected except for t h e average resultant head of liquid in t h e viscometer. Let this head be equal t o x centimeters of liquid as t h e liquid flows from left t o right, so t h a t in this case pz b u t t h e total pressure becomes equal t o $ 0 when the liquid flow from right t o left t h e pressure must be P o - p x . F r o m equation (2) we obtain t h e following equations.
+
Po-px
17 =
+ C/P/t2 Ctz
q
C'p
-Giz+Ctzz
whence
I n obtaining this correction t e r m i t is sufficient t o use t h e approximate value of C obtained b y using equation (2) with $ 0 in place of p . I n subsequent calculations i t is necessary t o know t h e specific gravity of t h e liquid t o be measured in order t o make t h e necessary pressure correction a n d also in order t o make t h e kinetic energy correction, b u t i t is t o be noted t h a t if t h e construction of t h e viscometer a n d t h e measurem e n t has been properly done these correction terms will both be small; hence, t h e specific gravity need be only approximately known, which constitutes a great advantage of this method. If t h e viscometer is constructed of t h e same material throughout, t h e coefficient of expansion of t h e material need n o t be taken into account, as m a y be easily verified b y introducing t h e coefficient of expansion into the dimensions in equation (I). B u t we cannot legitimately assume t h a t t h e same is t r u e of a n y changes in t h e dimensions of t h e a p p a r a t u s due t o t h e solubility of t h e glass. For this reason t h e t i m e of flow of t h e liquids used in calibration should be redetermined occasionally. However, so far as is known t o t h e author, t h e most prolonged use of a given instrument h a s never yet shown a change in t h e time of flow which could be attributed t o this cause. I n conclusion, we believe t h a t this viscometer is capable of a higher degree of precision t h a n t h e forms usually employed a n d t h a t a t t h e same time i t is easily made, convenient t o use, a n d economical of time. T h e corrections which have been discussed are small in this t y p e of apparatus, so t h a t t h e calculation of t h e viscosity b y means of equation ( 2 ) is simple. RICHXONDCOLLEGE,RICHMORD, VA.
MODIFIED HEMPEL PIPETTES By R. P. AXDERSON Received November 7, 1913
T h e chief objection t o t h e present form of t h e Hempel pipettes lies in t h e fact t h a t small drops of t h e reagent collect in t h e capillary while t h e gas is i n t h e pipette a n d are carried over into t h e burette on t h e return of t h e gas. This causes n o appreciable error when water is used as t h e confining liquid, b u t is ob-
For example, let i t be assumed t h a t there is 0.1 cc. of water on t h e mercury in t h e burette a n d t h a t about 0 . 0 1 3 cc. of alkaline pyrogallol is carried into t h e
v
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 CIIEMISTRY
23'3
enlargements. The length of t h e horizontal portion of t h e capillary tube is such t h a t t h e pipette fits i n t h e frame designed for t h e original form. This horizontal portion can be shortened somewhat by bringing t h e first bulb of tlie pipette over t o t h e left edge of t h e pipette frame a n d changing t h e f o r m of t h e frame accordingly. It was not thought desirable t o extend t h e capillary t u b e in a vcrtical direction' from t h e first bulb of t h e pipette since t h a t would necessitate t h e use of a longer capillary i n making t h e connection with t h e burette. These pipettes a r e furnished by Greiner a n d Friedricbs, Stiitzerbach i n Thiiringen, Germany. I n ordering, emphasis should be laid upon t h e actual size of t h e enlargcmcnt, since on account of the magnifying action of t h e glass, a n enlargement egpa?oally 3 mm. in diameter is considerably less t h a n t h a t , and is not a s satisfactory a s t h e larger one. CORNELL UNTYERSTIY, Il(ii~c.+.N. Y.
Val. 6, E o . 3
material. I n t h e diagram, R indicates t h e bank of lamps, which is used on account of bcing both inexpensive a n d easily adjusted to definite resistancc. A t binding posts A and B connection is made with t h e electric light system of t h e building. Bctwecn C a n d D is inserted the No. 24 nickel-chromium resistance wire E , a n d F is t h e switch. After the !amps R are loosened sufficiently t o break their connection, the switch a t P is turned on, a n d t h e lamps are screwed in one a t a time until the wire E is a dull red. The glassware which has been preparcd with guide wire is given a slight file scratch of about one-quarter inch length on t h e line t o be followed in cutting, a n d is brought into tlie loop E a n d revolved two or threc times, holding the nickel-chromium wire
AN EFFICIENT METHOD, FOR CUTTING GLASS By J. 1. Ilanny Received December 8, 11113
There is often great difficulty in satisfactorily cutting glass in t h e scientific laboratory, a n d this is especially t r u e i n t h e case of glassware of large-diameter. Tliere are several methods in common use. Probably t h e fine s a m e of t h e blowpipe applied upon a file scratch is one of t h e best known methods. The diamond point is often used with satisfaction. A metal rod m a y be bent to t h e shape of t h e object t o be cut, heated red h o t , a n d passed over t h e surface on t h e line where t h e glass is t o be cut, then if t h e glass is plunged into water it will separate on this line of contact. There is a method by Kum: using a n electrically heated nickel vire on a rather complicated apparatus which requires a n electric current of about E
~~~~
F-
eleven amperes. In this method a iew drops of water are applied to t h e heated glass, causing i t toecrack. The writer believes the following method t o be capable of wide application, a n d t h a t t h e desired results can be rapidly a n d efficiently obtained in t h e average laboratory. T h e equipment consists of a n electric system giving a t least six amperes electric current, a resistance apparatus consisting of a rheostat or a bank of twel\-e lamps (16 c. p.) arranged in parallel, a n d a piece of No. 24 nickel-chromium wire. When long tubing is to be cut, a steady rest will prove helpful a n d can be arranged t o snit t h e convenience of t h e operator. The method of procedure is a s follows: . Bind a piece of wirc around t h e glassware, twisting t h e ends together a n d making sure t h a t t h c wire follows t h e line where t h e glass is to be cut. This wire serves only as a guide, a n d m a y be of a n y inexpensive See White and Csmpbell. 1.A . C. S.. a7 (1905). 734. Chrm. Zi& 81. 406--407
I-Graduated Cylinder, cnt above I I,. mark. 2-2.5 L. bottle. 3-sirniiai $0 2. 4-2 L~Erlenmeyer Flask. 5-Battery Jar, cut in. below break. 6 and 9-Jena beakers I L. and 150 cc. 7-Brittle Thin-walled Tlubing. poor grade 01
close t o t h e metal guide. Aiter t h e glassware has been revolved two or three times in t h e loop E more lamps are connected in the bank R until t h e wire E is a bright red. Row t h e wire loop E is held in contact Nith t h e file scratch for a few seconds until a crack is started. T h e glassware is now revolved, keeping t h e heated wire slightly ahead of t h e crack until t h e glass is c u t off. If t h e wire cools i t may be released slightly from t h e glass until i t regains its heat. This method is very effective a n d can be used t o cut s t h e best a n y kind of glass from cheap bottle g l ~ to Jena. It will work successfully on glassware with 'cylindrical, spherical or conical walls, a n d will c u t t h e glass in a n y direction in which t h e guide is placed. A z ' / ? liter bottle was split (after having its neck c u t off) horizontally, although i t required more time t h a n a n y of the ordinary glass-cutting problems because of the thickness of t h e bottom of t h e bottle. The accompanying photograph shows nine samples which were c u t by this method in about one-half hour. AORICULTTBAI. Exr~nrmexrS T ~ I O N KNOXYILLS
UNIVExSI1Y OB THNNGssBB.
APPARATUS FOR TAKING DUST AND BACTERIA SAMPLES OF AIR BY CWARLES BASXBRVILLR Received February 12. l o l l
I n t h e investigation1 of t h c air of t h e schoolrooms of New York City, carried on with Professor C.-E. A. Tinslow a t t h e request of t h e School Inquiry Committee of t h e Board of Estimate a n d Apportionment, i t early became apparent on account of t h e large nnm1
See Tars Jooana~.this issue. p. 251.
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