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
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enlargements. The length of the horizontal portion of t h e capillary tube is such t h a t the pipette fits i n the frame designed for the original form. This horizontal portion can be shortened somewhat by bringing the first bulb of tlie pipette over t o the left edge of the pipette frame and changing the form of t h e frame accordingly. It was not thought desirable t o extend the capillary tube in a vcrtical direction' from t h e first bulb of the pipette since t h a t would necessitate the use of a longer capillary i n making t h e connection with the burette. These pipettes are furnished by Greiner and 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, an enlargement egpa?oally 3 mm. in diameter is considerably less t h a n that, and is not as satisfactory as t h e larger one. CORNELL UNTYERSTIY, Il(ii~c.+.N. Y.
Val. 6, E o . 3
material. I n the diagram, R indicates the bank of lamps, which is used on account of bcing both inexpensive and easily adjusted to definite resistancc. A t binding posts A and B connection is made with the electric light system of the building. Bctwecn C a n d D is inserted the No. 24 nickel-chromium resistance wire E , and F is the switch. After the !amps R are loosened sufficiently t o break their connection, the switch a t P is turned on, and the 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 the line t o be followed in cutting, and is brought into tlie loop E and 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 the scientific laboratory, and this is especially true i n t h e case of glassware of large-diameter. Tliere are several methods in common use. Probably the 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 may be bent to the shape of the object t o be cut, heated red hot, and passed over the surface on the line where the 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 an electrically heated nickel vire on a rather complicated apparatus which requires a n electric current of about E
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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, and t h a t the desired results can be rapidly and efficiently obtained in the 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 the operator. The method of procedure is as follows: . Bind a piece of wirc around the glassware, twisting the ends together and making sure t h a t thc wire follows t h e line where the glass is to be cut. This wire serves only as a guide, a n d may be of any 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 the metal guide. Aiter the glassware has been revolved two or three times in the loop E more lamps are connected in the bank R until the wire E is a bright red. Row t h e wire loop E is held in contact Nith the 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 the crack until the glass is cut off. If the wire cools i t may be released slightly from t h e glass until i t regains its heat. This method is very effective and can be used t o cut any kind of glass from cheap bottle g l ~ to s t h e best Jena. It will work successfully on glassware with 'cylindrical, spherical or conical walls, and will cut t h e glass in any direction in which the guide is placed. A z ' / ? liter bottle was split (after having its neck cut off) horizontally, although i t required more time than any of the ordinary glass-cutting problems because of the thickness of the bottom of the bottle. The accompanying photograph shows nine samples which were cut 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 the investigation1 of thc air of the schoolrooms of New York City, carried on with Professor C.-E. A. Tinslow a t the request of the School Inquiry Committee of the Board of Estimate and Apportionment, i t early became apparent on account of the large nnm1
See Tars Jooana~.this issue. p. 251.
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