1iVDUSTRIAL A i i D Eh7GIA’EERIh’G CHEMISTRY
174
Vol. 21, No. 2
Figure 4-Frequency Distribution (Arsenic per Unit of Apple Surface)
Gmtns
Figure 3-Frequency
/L,&
per
pound of h u r t
Distribution Pound)
(Arsenic per
Under the conditions of this investigation the results are accurate to one unit in the second significant figure. Substituting in the equation, it is seen that to gain this accuracy for the mean would require a sample of 120 apples. An accuracy of 2 in the second figure (15 per cent for this mean) could be obtained from 30 apples. For an accuracy of 5 per cent (1.5 units in the second significant place) 50 apples will suffice. It will probably be necessary to carry out further investigations to determine whether 50 apples can be picked from-an orchard with sufficient degree of randomness to obtain a representative sample. Summary
Individual analyses of 300 apples from 4 trees showed for individual apples ranges in arsenical residue of from 0.001 t o 0.031 grain arsenic per apple, the mean being 0.011. The
Collapsing Temperatures of Various Kinds of Laboratory Glass Tubing‘ A. W. Laubengayer CORNBLL UNIVERSITY, ITHACA, N. Y.
I Ntemperatures, designing glass apparatus that is to be used a t elevated it is desirable and oftentimes necessary to know beforehand the temperature to which the glass may be heated without becoming soft enough to collapse. The following experiments were made to secure this information, the tests being so carried out as t o duplicate, as nearly as possible, the conditions under which the glass is ordinarily used. The glasses tested were: an easily fusible soda-lime glass made by Greiner and Friedrichs, the “ R ’ glass (resistance glass) made by the same firm, Pyrex glass, Jena combustion tubing, Bohemian combustion tubing, and Moncrieff combustion tubing. Tubes with a bore of 13 mm. and a wall thickness of 1.8 mm. were used. Each glass was subjected to two tests. In the first, a tube, 1
Received December 10, 1928.
ratios for weight were from 0.004 grain to 0.095 grain arsenic per pound of fruit, with a mean of 0.031 grain. The range in area was from 0.05 grain to 1.30 grains per 1000 square inches of area of fruit, the mean being 0.43 grain. A formula is given for calculating the area of an apple from its weight which yields results differing not over 5 per cent from the best mechanical measurements. A statistical study of the data indicates that, in order to obtain a result with a probable error of 5 per cent in the value for mean arsenical residue per pound of fruit, it is necessary to analyze a sample of approximately 50 apples picked a t random. Acknowledgment
This investigation was undertaken a t the suggestion of R. C. Roark, Chief, Insecticide Division, Bureau of Chemistry and Soils. Acknowledgment is made to C. hl. Smith and G. L. Bidwell of the Food, Drug, and Insecticide Administration, U.S. Department of Agriculture, for helpful criticism. The apples used in this investigation were furnished by E. J. Newcomer (Yakima, Wash.) of the Bureau of Entomology, U. S. Department of Agriculture.
open at both ends, was heated in a n ordinary electric tube resistance furnace, and the temperature was noted by means of a chromel-alumel thermocouple which was placed in the furnace beside the tube. The temperature was quickly raised to 300 a C. and then uniformly a t the rate of 3 degrees per minute until the tube collapsed. The temperature a t which the first signs of collapse were observed was recorded. In the second test the tube was sealed a t one end, evacuated t o 3 mm. pressure, and then heated under this diminished pressure, the collapsing temperature being noted as in the first test. The results are tabulated below. GLASS Soft “R”soda lime Pyrex Jena Bohemian Moncrieff This glass devitrified readily.
COLLAPSING TEMPERATURE Open tube Evacuated tube
c.
700 760
820
860 860 820
c. 585
635 670
720 740 7700
I t should be noted that in these tests the tubes were heated for a comparatively short time. If the glass were subjected to longer periods of heating, the temperature of collapse would probably be somewhat lower. To avoid collapse of a tube, it should not be heated higher than 50” below temperatures given in the table.
