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 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
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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, 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 i t s heat. This method is very effective a n d can be used t o cut a n y 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, 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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Mar., 1914
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 C H E M I S T R Y
ber of samples t o be collected. in widely separated schools perhaps on t h e same day, t h a t i t would be necessary t o depend upon some other method t h a n one relying upon t h e use of a h a n d p u m p in conjunction with a gas meter. T h e limited time per day (school hours) available for collecting samples a n d t h e transportation of apparatus were factors of supreme importance. After m a n y conferences, in which t h e entire staff took p a r t , Xlessrs. TTallace a n d Tiernan, Engineers,
New York City, who also h a d a representative present, supplied us with a n apparatus, which we think should be described for t h e benefit of those members of t h e Society interested in atmospheric hygiene. T h e principle of t h e a p p a r a t u s depends upon measuring volume b y time. T h e apparatus includes a n exhaust p u m p of t h e friction type r u n by a l/32 horse power motor a n d a measuring apparatus of compact a n d ingenious design. This apparatus, placed be-
tween t h e p u m p a n d t h e sampling filter, consists of an air chamber, t h e inlet of which is connected with t h e t w o ends of a U-tube, graduated on i t s distal arm. The opening of this distal a r m is so reduced t h a t t h e pressure a t t h e mouth of t h e proximal a r m is registered b y a rise of t h e liquid in t h e distal a r m . T h e whole apparatus is enclosed in a n oak box fourteen inches b y twelve inches, air being drawn in through a n opening a t t h e t o p a n d forced o u t through a n opening in t h e side. T h e upper opening is fitted with a small steel cup with a rubber stopper inside, having a hole large enough t o fit t h e constricted end of t h e sugar or sand filter. At t h e base of t h e cup, a n extension passes through t h e wooden cover a n d screws on t o t h e suction chamber of t h e machine T h e apparatus as first made was designed t o draw through about three-quarters of a cubic foot of air per minute. With t h e resistance due to t h e sand or sugar, however, t h e time required was about three minutes per one cubic foot. T h e p u m p when first tested proved t o be t o o noisy, so t h e apparatus was placed within a second box lined with felt a n d a muffler attached to t h e exhaust. This reduced t h e noise t 0 . a minimum. Teachers in whose classrooms we operated, were consulted, a n d no objections were offered t o t h e noise made b y t h e apparatus during class hours. T h e accuracy of obtaining dust a n d bacteria samples by means of this form of apparatus was compared with t h e hand p u m p a n d meter method and approximately similar results were obtained. A further check was made by running t h e electrically driven p u m p a n d measuring t h e flow by means of standard gas meters. Both t h e electrical p u m p a n d t h e gas meters were tested a n d standardized b y t h e manufacturers. T h e amounts of air taken for samples for bacteria a n d dust with this machine were usually three feet a n d two feet, duplicate determinations always being made. T h e official methods of t h e Public Health Association were used in making counts of bacteria a n d studying t h e character of t h e dust collected. T h e apparatus might be used extensively i n studying t h e air of factories a n d other places where occupational diseases are t o be investigated. COLLEGE OF THE C m OF NEWYORK
ADDRESSES RECENT DEVELOPMENTS IN COMMERCIAL EXPLOSIVES' E. A. LBSUEUR
The last few years have seen a great development in the use of safer explosives than were previously commercially available or even believed to be possible. It is my purpose to take a brief general view of the trend of development, to deal with some particularity with an explosive of rather unique character with which I have had much experience, and incidentally to outline certain advantages and disadvantages of the new types. The most striking feature among the changes occurring in the field is the almost omnipresence of nitrate of ammonia. Although a salt of a hypothetical metal it breaks down into a 1 Presented a t the 6th Annual Meeting of the American Institute of Ch emical Engineers, T h e Chemists' Club, New York, December 1&13. 1913.
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gaseous mixture containing a surplus of free oxygen and no solid residue whatever and, insofar, is therefore peculiarly suited to employment in explosives. Unfortunately it is very hygroscopic and of dep1or;fbly low specific gravity so that but a comparatively small weight can be packed into a given cavity. On the other hand, its adaptability, within the above limitations, is remarkably wide and we find it associated with almost every ingredient known to explosives manufacture, and especially with nitroglycerin. So wide is the present market for this material for use in explosives that practically the entire output of the gigantic Norwegian Atmospheric Nitrate works is now delivered in the form of nitrate of ammonia, and further importankdevelopments in the cheap manufacture of this important compound are to be looked for in the very near future. Perchlorates, and especially perchlorate of ammonia, have
