ANALYTICAL EDITION
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VOl. 3. No. 2
Determination of Barium .Fluosilicate Spray Resid ue’ R. H. Carter INSECTICIDE DIVISION,BUREAUO F CHEMISTRY AND SOILS, DEPARTMENT O F AGRICULTURE, WASHI~XGTON, D.
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HE introduction of substitutes for arsenical compounds
in the control of insect pests brings up the question of the determination of the amount of residue left on food products. Determination of the amounts of such compounds applied by different methods of spraying and dusting is also important from the standpoint of ascertaining the efficiency of the compounds and their weathering qualities. I n the Pacific Northwest barium fluosilicate was given extensive tests for the control of codling moth by E. J. Newcomer, of the United States Bureau of Entomology. The material used in these experiments was a commercial product containing about 80 per cent barium fluosilicate and 20 per cent fluffing agent. As there was no standard procedure for determining residues of barium fluosilicate it was necessary to devise one that was fairly rapid and as accurate as possible. There are, of course, four possible ways for determining the quantity of such a compound-i. e., analyses for (1) barium, (2) silica, (3) fluorine, and titration with standard alkali. The determination of silica under such conditions is entirely unsatisfactory. Commercial barium fluosilicate contains varying amounts of hydrated and partially hydrated silica, and a special light form of barium fluosilicate contains precipitated silica as a diluent. I n addition, considerable dust accumulates on fruit and foliage by the end of the season owing to the absence of rain so that determinations of silica are impossible. The determination of fluorine in small amounts is possible by several different methods, but none are entirely satisfactory. Some of the common. methods give results which are consistently too low, while others are too cumbersome and involved for use under these conditions. Titration of the barium fluosilicate with standard alkali is not practical owing to the impossibility of its removal as such from the fruit. The determination of barium under standard conditions is accurate and reliable, and as there was no danger of errors due to added barium from the fruit or foliage this was decided upon as the best of the four methods. There are two general methods for obtaining spray residue from fruit for analytical determinations: peeling and subsequent ashing or digestion of the peelings to destroy the organic matter, and washing with some solvent and analysis of the solution. The washing method, which is in common use for removal of arsenical residue, is much the more rapid and sufficiently accurate, so it was adopted. Because of its reaction with barium fluosilicate according to the equation BaSiFa
+ 4NaOH-BaFs
Jr 4NaF 4-Si(OH)r
a dilute solution of sodium hydroxide was decided upon as being a satisfactory solvent, and the following procedure was developed. Procedure
Samples of twenty apples of approximately uniform size were selected for analysis and the weight determined within 5 grams. They were then washed individually by immersion for approximately 30 seconds in a boiling 3 per cent sodium hydroxide solution and rinsed with slightly acidulated water. The combined rinsings and washing solution, I
Received December 1, 1930.
c.
totaling 400 or 500 cc., was then cooled, made strongly acid with hydrochloric acid, and filtered as rapidly as possible through filter paper. This filtration removed solid organic matter, etc., extracted from the apples during the washing process, and the filtrate was free of suspended matter but highly colored. The filtrate was made strongly alkaline with sodium hydroxide, then neutralized with sulfuric acid, and about 5 cc. in excess added to precipitate the barium as barium sulfate. The solution was boiled, cooled slowly, and allowed to stand 12 hours or longer. It was filtered through filter paper, the paper was washed, dried, and ignited in a muffle for 1 hour, and the ash weighed as barium sulfate, and then calculated to ljarium fluosilicate. Table I-Determinations
of Barium Fluosilicate Spray Residue
Check (3 lbs per 100 gdl, in 5 cover sprays)
BARIUM FLUOSILICATE AVERAGE Grainllb. Grain/lb 0 119 0.122 0 126
Check (4 lbs. per 100 gal. in 4 c6ver sprays)
0 129 0.129
0.129
Check (4 Ibs. per 100 gal. in 5 cover sprays)
0.145 0.144
0.144
Washed with 0.5 per cent NaOH
0 028 0.034
0.031
Washed with commercial alkaline compound (60 lbs per 100 gal.)
0 025 0 052
0.038.
Washed with commercial alkdline compound (40 lbs per 100 gal.)
0 041 0 067
0.054
Washed with 0.66 per cent HCI
0.082 0 077
0.080
0 086 0 085
0.085
0 090
0.103
0 087 0 115
0 101
0 041 0 049
0.045
Washed with 0.5 per cent NaOH
0 031 0 023
0.027
Washed with 0.5per cent NaOH s o h . after 1 hour’s use
0 031 0 046
0.038
Washed with 0.5 per cent NaOH s o h . after 2 hours’ use
0 058
0.054
Washed with 0.66 per cent HC1
+ kerosene emulslon
Washed with 0.33 per cent HCl
0 117
Washed with 0.33 per cent HC1 Wiped by hand
+ kerosene emulsion
”
0 050 Washed with 0.5 per cent NaOH s o h . after 3 hours’ use
0 039 0 031
0.035
Washed with 0.5 per cent NaOH s o h after 4 hours’ use
0 040 0 042
0.041
BaSiFs (4 lbs. per 100 gal )
0 109 0 124
0.116
0 116 0 118
0.117
0 112 0 128
0.119
0.115
0 116
+ 0 5 pint fish Oil) per 100 gal. + 1 pint fish per 100 gal. + 2 pmts fish oil)
BaSiFs (4 lbs. per 100 gal. BnSiFs (4 lbs RaSiFe (4 Ibs
Oil)
Although this method may be subject to some criticism, it was fairly rapid and gave results that were consistent and capable of duplication. The data in Table I, giving duplicate analyses on a number of samples, indicate its reliability and consistency. The results are calculated in grains of barium fluosilicate per pound of fruit’ in order that comparison may
April 15, 1931
INDUSTRIAL AND ENGINEEBlNG CHEMISTRY
be made with results on arsenical residue determinations. It should be remembered, however, in making such comparison that these results express approximately 80 per cent of the total residue, whereas arsenical residue results are always expressed in grains arsenic trioxide per pound, which in the case of lead arsenate is probably approximately 30 per cent of the total residue. One point to be remembered in following this procedure is that the volume of solution must be sufficiently large at all times to keep in solution all barium fluoride and barium fluosilicate that may be formed before the final precipitation of barium as barium sulfate. As shown in the table, these analyses were made on samples which had ,been subjected to considerably different treatments, including check samples which had received as many as five cover sprays, samples from the orchard immediately after spraying, and samples from commercial washing ex-
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periments with a number of different solvents on apples which had received five cover sprays of barium fluosilicate. Naturally, under such conditions considerable variation in duplicates may be expected, owing to variations in sampling. Actually, however, the agreement between the duplicate analyses was very close in most cases. The difference between duplicates which does not appear to be a function of the amount of residue, has a mean value of 0.011 grain per pound under the conditions of these experiments. This corresponds to an average error in the mean of duplicate determinations of *7 per cent when the total residue approximates 0.08 grain per pound. This is probably within the limits of experimental error in sampling. Based on these results this method may be considered sufficiently accurate and reliable to give at least comparative results for the determination of barium fluosilicate as spray residue on apples.
Further Applications of the Centrifugal -Filtration Tube' Evald L. Skau and Louis F. Rowe JARVIS
CHEXICAL LABORATORY, TRINITY COLLEGE, HARTFORD, CONN,
Experimental data here reported show that the is pressed flat on the disk and centrifugal filtration tube may be used satisfactorily folded well down over the tion tube, a simple confor the approximate estimation of solubilities at differedges. The disk is then trivance for the rapid ent temperatures. The binary freezing-point diagram pushed down upon the shouls e p a r a t i o n of solids from of the system benzene-naphthalene, which has been der B so as to fit snugly to liquids at any desired temperaconstructed by means of this method, shows fair the walls of the tube. ture, has been described in agreement with the accurate diagram. The mixture of known coma previous publication (a) and In such cases, as well as in water solutions of solids, position is now weighed into experimental data were there the eutectic composition may be estimated by a single the tube H , tube G is weighed presented to show its usefuldetermination by means of this device. This is proved and fitted into place, and the ness in purification by reby experimental results for the above system and for sample is melted completely crystallization, especially in the systems water-sodium nitrate and water-potassium by heating. The whole tube the case of compounds which iodide. is then immersed for from 20 require low-temperature techThe centrifugal filtration tube should be applicable to 30 minutes in a thermonic for their separation.2 The in any plant-control work in which, for example, it stat set a t the desired temadditional applications of this is desired to carry a reaction to a stage where a certain perature, t, being protected device are based upon the fact consistency or freezing point is reached. Instead of from contact with the liquid that it can be used to detera rough determination of the freezing point, a deterof the bath. mine the approximate promination of the amount of solid separated at some Note-For temperatures above portions of solid and liquid in 0' C. a rubber sac such as may be arbitrary temperature could readily be made with a mixture at any definite temmade by cutting off the end of a t o y suitable accuracy. perature. It can therefore be balloon is suitable. For low temused in certain cases for the peratures where rubber cannot be rough construction of binary freezing-point diagrams and for used, the tube may be inserted within another glass tube. the rapid estimation of eutectic compositions and temperat#ures, It is then inverted quickly and immediately centrifuged for and has practical applications in plant control work. a few minutes. The liquid is thus thrown into chamber G, the bulk of the separation being accomplished within 20 secRough Construction of a Binary Freezing-Point Diagram onds of the time when the tube was removed from the bathInstead of determining the freezing point of a given compo- that,is, before the temperature has changed appreciably. The sition, the composition of the mixture having a given freezing solid phase is now removed with the disk and the weight point is found-that is, a mixture of known composition is of the liquid in G ascertained. The solid phase must be brought to equilibrium a t the desired temperature (below its identified. primary freezing point) and the proportion of solid and Since this liquid was at equilibrium with the solid phase liquid determined. The composition of the liquid can then a t the temperature of the thermostat, its freezing point is t. be calculated. If the original mixture consisted of a grams of A and b grams A circular piece of filter paper about 1.5 cm. larger in of B , and if 8 b grams of solid B have been separated out by diameter than the perforated porcelain disk C (Figure 1) centrifuging, the liquid having the freezing point t has the is folded along a diameter and then slit with a pair of scissors composition a b - Sg part way across the perpendicular diameter starting a t the of A and of B a f b - S b a + b - S b center. The wire E is passed through this slit and the paper The mother liquor and the crystals may now be recombined 1 Received October 23, 1930. and another determination may be made at other temperaThese tubes are now obtainable from Eimer and Amend, New York.
HE centrifugal filtra-
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