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excess of other salts it may be necessary, in order to overcome the coagulating effect of the salts, to add more gum solution t h a n statid. Pliosphates, n-hich according- to Dodd (3) are often present when testing for borates, were found not to interfere with this test.
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Literature Cited (I) .4udibert, English Patent 241,186 (1925). (2) Bean and McLeary, “Chemistry and Practice of Finishing,” p. 446, Hutton, Hartley and Co., Manchester. 1926. (3) Dodd, A n a l y s t , 64, 282 (1929). :4) Tv’illiams, I b i d . , 63, 411 (1928).
Photographic Estimation of Foreign Materials in Gums and Resins’ E. 4.Georgi HERWLES EXPERI?~IEST.U. ST.ATICIY, HERCULES POWDER
E R T A I S analytical values are often foregone in a routine analysis, because it is felt that the time and cost of obtaining them overbalance their value. This does not mean, hovei-er, that they are worthless. The value for dirt in gums and resins undoubtedly often falls in this class. The following data are presented to show the advantages of using the microscope and camera as an aid in making such determinations.
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Analytical Procedure The method followed to obtain the quantitative results (Table I) was that outlined in the A. S. T. 11.Tentative Standards, D-269-27T for 1927, “Determination of Toluene Insoluble Matter in Rosin.’’ It is briefly as follows: 50 grams of freshly powdered rosin are dissolved in 150 cc. of hot toluene, filtered through a tared Gooch crucible, and mashed d t h hot toluene. The crucible is dried to constant weight a t 105” C. The increase in weight is the amount of dirt in the rosin. Photomicrographic Procedure
C O > l P a S Y , KENVIL, ?;.
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l l a k a m camera (Leitz) was used and a magnification of 30X was obtained on the 9 by 12 em. plates. Eastman’s Conimercial Panchromatic film was used throughout. Actually a lens of the llicro Tessar type is supposed to be used without an eyepiece. If used with an eyepiece a loss of definition and resolution is suffered; but it has been found that the increased depth of focus obtained, in this instance, more than compensatesfor these losses. Probably if a bellows camera mere available, somewhat better photographs could be obt,ained by using the Micro Tessar lens without an eyepiece, but this would add considerably to the cost and time of obtaining the photographs, as well as making i t very difficult to secure dark-field illumination. As mentioned before, however, these photomicrographs were obtained using a hlakam camera which fits into the draw tube of the microscope and has a fixed bellows. To put it in operation, therefore, requires little more time than to change an eyepiece. Transmitted light was obtained by means of a lamp with a 100-watt incandescent bulb, and a low X.A. condenser. Dark-field illumination was secured by inscrting a central stop beneath t’he condenser, while the rest of the set-up remained the same. It was observed with several negatives t’hat the exposure had been uneven in different parts. This was found to be due to reflections from the uneven bottoiii of the crystallizing dishes used, but detracted only from the appearance, and not the accuracy, of the photograph.
Sereral average lunips of rosin are chipped to reniole the outside layer and broken into small lumps, several of which are melted in a crystallizing dish until a layer 4 to 5 inni. thick is obtained. The dish should have a flat bottom with plane surfaces, as an uneven bottom is liable to cause undesirable shadows in the photograph. An alternative method Discussion of Results consists of powdering a large sample and melting a weighed quantity of this powder. I n this instance the container The results show that this method of analyzing rosin must be always of the same dimensions. Care should be samples for dirt is for all practical purposes just as accurate taken not to get the rosin-too hot, or the dirt will tend to as the usual quantitative analytical procedure. This is borne settle out on the bottom of the dish before the rosin can cool out by a comparison of the results in Table I with the amount and stiffen enough to hold i t in suspension. X sample pre- of dirt seen in photographs 1 to 16, Figures 1 and 2. pared as above is then observed under the microscope. ‘This Table I-Toluene-Insoluble Material in Gums and Rosins as examination, preferably a t several different magnifications, Determined by Analysis determines the quality of the preparation-i. e., 151iether TOLUTOLUESE ENE or not it contains air bubbles or if the dirt has segregated, SAMORIGIX OF INSOLUSAMORIGIS OF INSOLUctc.-and shows the appearance of the average field. This PLE SAMPLE GRADE BLE PLE SAMPLE GRADE BLE Per cent Per cenl “average field” is photographed a t a definite magnification, 1 Commercial 9 Greek gum K 0.050 preferably with both transmitted and dark-field illumination. abietic acid 0.002 10 American gum N 0.069 2 Wood rosin I 0.003 11 American gum WG 0.080 It has been found, however, that the distribution of dirt 3 Wood rosin FF 0.006 12 American gum I 0.093 particles throughout the sample, with the exception of large 4 American gum K 0.019 13 American gum G 0.10 5 Spanish gum S 0.022 1 4 American gum D 0.12 pieces. is usually quite uniform. Most attention, therefore, 6 American gum WW 0.028 15 Portuguese gum I 0.13 7 French gum W W 0 028 must be paid to the occurrence of large pieces of bark, wood, 8 American gum H 0 . 0 3 % 16 American gum F 0.17 etc. Figure 1 shows sixteen photomicrographs taken with transAt times the dark-field and transmitted-light photographs mitted light, while Figure 2 shows the same fields under do not match. This is caused usually by two things. First, dark-field illumination. The original photographs were ob- there is a difference in optical quality of the different kinds tained with a Bausch Bt Lomb 32-mm. Micro Tessar a t f. 11, of dirt present. That is, a piece of iron rust or bark will in conjunction with an 8 X Periplan Leitz eyepiece. A photograph dark or black by both methods of illumination, while pieces of sand or wood fibers will photograph dark 1 Received March 26. 1930.
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with transmitted-light but light with dark-field illumination. Second, the great increase in contrast obtained by using dark-field illumination serves to bring out and make visible much more of the finer particles of dirt. Estimation of the total amount of the different kinds of material in the rosin by consideration of the above details will lead, therefore, to a more accurate idea of the total weight present. I n this work, however, it has been found that the
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dirt or foreign materials run fairly uniform as t o composition. Furthermore, the results give a picture of the impurities present, as well as telling the nature of the material. The actual accuracy or duplicability of results is dependent on correct sampling, as is any quantitative procedure. It should be mentioned, however, that while the amount of material actually photographed is small in comparison to the amount used in the A. S. T. AI. method. the sample from
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which the photograph is obtained may be of any desired amount and is only limited by the size of the container. By stirring the sample and then cooling quickly a very even distribution of the dirt is obtained. Advantages of Method
Some of the advantages of this method have just been indicated. Its biggest advantage, however, is the great saving
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in cost. Whereas the average cost of duplicate runs (in this laboratory) following the A. S. T. N. method is approximately five dollars, two photographs can be obtained for a cost of one dollar, including time and labor. I n addition, final results can be obtained in almost half the time. The finished results are in pictorial form, which gives the user a sense of closer contact with his raw materials or finished products. Also, the photographsmay be a distinct advantage
ANALYTICAL EDZ TIOS
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in certain industries where particle size of impurities is liable to be of importance. For example, a soap manufacturer might allow 0.1 per cent of dirt, provided none of it had a particle size greater than 50 microns. Applications of Method The outlined method is quite flexible and is capable of application in many other ways. It is not limited to a n examination of the dirt in gums and resins; the dirt in many other materials, such as glue, gelatin, etc., can be determined by i t with equal ease. Higher magnifications can be used for smaller particles.
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Dirt in the material might be allowed to settle for a definite length of time before photographing, and thus allow analysis for just the dirt above a certain particle size by obtaining it in a single plane. If all photographs are taken under constant conditions, including the same exposure time, a good idea of the transparency and color of the material may be obtained from the density of the negative. If a comparison microscope is a t hand, the sample under observation may be compared directly with a standard or another saniple of the same material. "le-The discussion of results applies only t o t h e original photographs I t should be remembered t h a t the originals have su5ered somewhat both in making the composite pictures and also in reproduction of same.
Method for Determining Carbon Dioxide in Carbonates' C. A. Jacobson a n d J o h n W. Haught WEST VIRGINIA UNIVERSITY, ~ I O R G A K TW OW . V.4. N,
OR many years it has been the prkilege of one of the
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vriters to test a number of the most highly reconimended methods for determining carbon dioxide in carbonates and to evaluate their merits. This was accomplished in connection with a course in advanced quantitative analysis a t the K e s t Virginia Uaiversity. I n order to ascertain the degree of success the average student would have in analyzing a limestone or dolomite by a given method, the same sample was submitted to groups of students to be analyzed by different methods. Upon checking over the results it was concluded that a modificationmight be made so that better and more uniform results lvould be obtained by the analyst who is not an expert in this field.
A p p a r a t u s for D e t e r m i n i n g C a r b o n Dioxide i n C a r b o n a t e s
an inch from the bottom of the flask. The separatory funnel is in turn fitted 11 ith a glass-stoppered absorption tube, C, containing Ascarite provided t o remove carbon dioxide from the aspirated air after the reaction is over. The condenser is made by cutting off the closed ends of t n o sniall bideneck test tubes and fitting the cut ends together nith a piece of rubber tubing. Tube E serves the dual purpose of absorbing most of the moisture from the carbon dioxide and permitting the regulation of the flow of gas through the apparatus. The U-tube F is filled with Dehydrite for the purpose of taking out the last traces of water. The lon-er compartment of the Fleming absorption tube, G, is filled with Ascarite and the upper compartment with Dehydrite, which serves to retain any moisture that niay he formed in the Ascarite bulb during the carbon dioxide absorption. G should be of such a size that its weight when filled shall not exceed 100 grams. The upper end of the Fleming bulb is connected with the suction tube, H , connected either with a filter pump or a n aspirating bottle by mean5 of a glass stopcock inserted between G and H for the purpose of regulating suction. Procedure Before the determination is started the apparatus is carefully tested for leaks by applying suction a t H . -4bubbler (not shown) is inserted between G and H for this test and then removed. Leaks are seldom encountered, however, if the glass-stoppered joints have been previously tested. All rubber connections are made by heavy wall pure gum tubing. The rubber stoppers used are small, which more readily permit of making tight joints. Having proved the apparatus tight, about 3 to 4 cc. of water are added to the samplr (about 0.7 gram) through B, after which about
