I N D U S T R I A L A N D ENGINEERING CHEMISTRY
50
acid than sulfuric or it may be the result of the specific action of the chloride ion, which the writer has found to be very destructive of protein matter in concentrated solution even a t the point of neutrality, while sulfates appear to have a preservative action. The test tube experiment was repeated for vegetable-tanned leather, but no destructive action was apparent to the eye
Vol. 18, No. 1
with solutions weaker than about 8 N . The degree of chrome tannage appeared to have no appreciable effect upon the action of the acid so long as the leather had been sufficiently well tanned to stand the boiling test. There are many and obvious ways in which this work can be extended so as to make possible intelligent specifications for acid content of all kinds of leather.
The Relative Toxicity of the Arsenates of Calcium' By S . B. Hendricks, A. M. Bacot, and H. C. Young DELTA LABORATORY, U. s. BUREAU OF ENTOMOLOGY, TALLULAH, LA.
ALCIUM arsenates were first used as insecticides by Bedford and Pickering2 and by Smith.3 Since that time, especially through the experimental work of C ~ a d calcium ,~ arsenates have' become extensively used as insecticides. Some work of a fragmentary character has been carried out comparing the toxicity of calcium arsenate with that of other arsenicals. Ricker5 found calcium arsenate (commercial) to be as effective as crude AsmOsor Paris green. Lovett and Robinson6 compared the toxicity of calcium arsenate with lead arsenate. Cook and McIndoo7 made a similar comparison with some other arsenicals. The present research deals with the comparative toxicity of the various arsenates of calcium, representing an endeavor to further stabilize the manufacture of calcium arsenates and to obtain a closer relationship between the analysis of a definite commercial product and its toxicity to certain insects. Quantitative results can be obtained in this type of research, but very little data of any value can be found in the literature.
C
Experimental
Locusts (Melanoplus femur Rubrum) and boll weevils (Anthonornus grandis Boh) were used as experimental insects. The locusts were adults that had been collected in the field. They were free from disease and parasites, the check mort'ality never exceeding 5 per cent and seldom being that great. Ten locusts were placed in a wire cage 30.5 X 30.5 X 3.8 cm. and were fed on a standard bran mash containing 24.0 grams of wheat bran, 12.5 grams of sugar, 1.0 gram of the poison to be tested, a few drops of amyl acetate, and sufficient water to moisten 'the mash thoroughly. The check determinations were fed on a similar mixture with the exception of the poison. Observations to determine the resulting mortality were made a t &hour intervals. Clean paper was placed beneath the cages in order to catch the feces. Bt t'he end of an experiment the locusts were treated with dilut'e acid, dried, and reserved for analysis. The feces were carefully collected and kept for analysis. I n the case of the boll weevils three tests were madedust on wet leaves, dust on dry leaves, and spray. The wet leaves were fresh cotton leaves from which the petiole had 1 Presented as a part of the Insecticide and Fungicide Symposium before the joint session of the Divisions of Agricultural and Food Chemistry and Biological Chemistry at the 70th Meeting of the American Chemicdl Society, Los Angeles, Calif., August 3 to 8 . 1925. 2 Lead Arsenate, 8th Rept. Woburn Expt. Fruit Farm, 1908, pp. 15 and 17. 8 Rept. N. J. Agr. Expt. S t a . , Entomology Dept., 1907, p. 476. 4 U.S. Defil. Agr., Circ. 162 (1921); 875 (1920). ' J . Econ. Enfomol., 12, 194 (1917). J . Agr. Research, 10, 199 (1916). I U.S.Depl. Agr., Bull. 1147, 30 (1923).
been removed in order to necessitate surface feeding. These leaves were dipped into rain water and immediately dusted with the preparation to be tested, the poison being shaken from a bottle over which several thicknesses of cheese-cloth had been placed. Only the upper surfaces of the leaves were treated. I n the case of dry leaves the leaves were dusted after wetting and then allowed to dry before the introduction of weevils. The sprayed leaves were prepared as directed above, the poison being applied by dipping into a suspension of the arsenical. The suspensions contained the equivalent of 2 pounds of poison in 50 gallons of water. Lantern globes, covered with one thickness of unbleached domestic and placed upon an unglazed earthenware dish, which contained about 1.5 inches of sand, were used for experimental cages. The sand was kept moist at all times. The leaves were placed in the globes, the base of the petiole being pressed into the sand, and ten field-collected weevils were released. Observations were made a t frequent intervals to determine the resulting mortality. Dead weevils were removed after each observation and reserved for analysis. The tests extended over a period of 48 hours. Table I-Analysis
Expt.
COMPOUNDS
CaHAsOd.HzOo CasHz(As04)4.4HzOb Car(AsO4)z.EHzOb Caa(AsOa)z.HzOcand 3Ca3(AsO+)z.Ca(OH)zd Ca(0H)z Ca(Ca0H)AsOi Ca(0H)zf
6-0
of Compounds
Free CaO in Ratio CaO AszOs C o t CaO comb. Per Per Per Per CaO: Per As201 cent cent cent cent cent 0 S o h . containing 0.268 gram AszOs per cc. 0.0757 gram CaO per cc. Solution {containing 10.3248 gram AszOs per cc. 2 2 8 . 2 0 5 7 . 8 5 0.00 0.00 2 8 . 2 0 2.5 34.80 5 6 . 2 5 0.00 0.00 3 4 . 8 0 3 31.22 42.00 0 . 4 0 0.00 3 0 . 7 2 3 3.33 4 a
51.00 4 0 . 0 0 0 . 4 2 2 1 . 1 6 2 9 . 3 0 40.35 41.20 5 . 3 2 0.00 33.58 45.00 40.88 0.62 4 . 7 1 39.50 96.7
Methods of preparation of the compounds: 0 Smith J . A m . Chem. Soc. 42 259 (1920). b Lime-kater and dilute HaAsOn, alkaline to phenolphthalein. allowed t o stand for several days and filtered. c Caa(AsOa)z.EHzO, prepared by method (2). dried a t 200' C., lime added. d Tartar, Wood, and Hiner, J . A m . Chem. SOC.,46, 809 (1924). e To be described in a later publication by Smith. I C. P . lime. o Analysis made by the method of Smith and Hendricks, THISJOURNAL, 16, 950 (1924). ~~
Table 11-Toxicity Bran mash conAv. sumed longevity NO. Hours Expt. expts. Gram A 10 3 2 . 9 =t 0 . 5 0 . 0 0 5 0 B 10 3 1 . 6 t 0 . 8 0 . 0 0 7 1 3 7 . 2 =t 0 . 9 0 . 0 0 2 6 c 10 3 4 . 0 =t 1 . 3 D 5 4 1 . 9 1. 1 . 0 0 . 0 6 4 9 E 10 4 3 . 7 =t 0 . 9 0 . 0 0 3 3 F 10 5 8 . 9 1. 2 . 0 0 . 0 0 3 6 G 5 H 10 7 7 . 5 =+ 1 . 8 0.0087
of th e Locust AszOs in body Mg. 0.132 0.102 0.038 0.107 0.052 0.034 0.037 0.067
AS205 in
feces Mg. 0.0020 0.0013 0.0013 0.0021 0.0031 0.0015 0.0031 0.0279
Ratio AszOs in body As205 in feces 65.4 81.0 30.4 51.0 17.0 -. . -
22.2 12.0 2.4
IiVD USTRIAL AND ENGINEERIXG CHEMISTRY
January, 1926 T a b l e 111-Toxicity
of the Boll Weevil
2Ca(CaOH)As04
As206 in Numer- bodv of ---AVERAGE LONGEVITY, HOURSical av. one weevil Suspensions of av. (av. of 2 Ibs. in 50 longev- 3 tests) No. Dust on Dust on Expt. wet leaves dry leaves gals. ity Mg. expts. 6 A 0.0017 6 0.0017 B 18 i’.b 0.0025 C 10.7’+‘1.2 28 18 D 10 * 0.8 28 i: 1.1 0.0021 18 0.0010 E 23.0 f 1.2 32 * 1.6 18 F 25.5 f 1.5 34 f 1.2 0.0013 18 0.0010 G 15.0 f 0.7 25 f 0.8 30.2 f 1.4 0.0020 18 H 24 2.0 Nontoxic 12 I 33 dead in 58 10 dead in 57 .... 1s J 26 dead in 56 7 dead in 59 7 dead ;n 59
....
f
The analyses were made by the Gutzeit method, the organic matter being destroyed by digesting with nitric and sulfuric acids. The compounds listed in Table I, representing all known compounds in the system CaO-Asz06-H20, were used during the tests. Discussion of Results
An inspection of Tables I1 and I11 will show that both the average longevity and the ratio of As205 in the body to Ass05 in the feces serve as criteria of toxicity. The variation from the mean value is greater in the latter case, however. These -results directly confute the statement of Moore; indeed his own results are contradictory to his conclusions.8 The following table and paragraph are quoted from his bulletin: Lead arsenate added t o bran mash Gram
.,
Bran consumed before death Gram
(1)
(2) .,
0.02 0.04 0.10 0.20. 0.30
0.0300 0.0210 0.010s 0.0090
0.0070
Ratio
Excreta Hours t o kill (3) 66.5 92.2 69.5 55.5 58.0
Body (4)
1.0000 1.0898 1.2005 1.2502 0,9092
The hours required to produce death vary greatly, while the quantity of arsenic consumed is reduced rapidly. On the other hand, the results are affected but slightly by great differences in the quantity of poison fed t o the locust.
It is admitted that (2) does not serve as a criterion for toxicity, but (3) and (4) do, as is shown by a closer consideration of Moore’s data. The average longevity, discarding the second result since it is more than five times the probable error, is 62.5 *2.3 hours, an error of 3.7 per cent; whereas 0.04, discarding the last two figures of the ratio is 1.09 each observation, since they are insignificant, an error of 3.6 per cent. Even including the second observation the probable error in the average longevity does not exceed 5 per cent. This consideration should be sufficient to show the errors in the above work and to reestablish the use of‘ the average longevity as a correct criteria for determining the relative toxicity of arsenicals. Moore has brought out one very good point, however, in criticizing the other methods that have been used so often in previous investigations. I n the writers’ experiments, with but one exception-and even in this case the probable errors overlapped-the average longevity and the ratio checked as criteria of toxicity. Extremely small doses no doubt would show a slight increase in the average longevity, but they would also show less unassimilated arsenic in the body. Both criteria are certainly satisfactory when the rate of dosage is constant. Increase in basicity decreases the toxicity of a calcium arsenate to the locubt, the greatest change occurring after Caa(As04h.xHz0. This is probably due to the fact that the basic arsenates must be partially hydrolyzed to the compounds giving more “soluble” arsenic before toxic results are produced. A similar explanation is probably correct in accounting for unusual burning produced on plant surfaces by calcium arsenates, thus: 8
University of Minnesota, Agr. Expt. Sta., Tech. Bull. 2, 41.
+
Ca(HCOa)z
51 -+
+ +
Caa(AsO4)~ 2CaC03 2H20
The presence of Ca(HCO& as an excretion of surfaces of malvacae plants has previously been reported by Smith.g When the CaO is not in combination with the arsenic, however, the toxicity is not affected. A comparison of case F and E will illustrate this point. I n each case the mol ratio CaO:AssO5 in combination is the same, 3, and the toxicity is the same within the limit of error. I n F , however, the apparent mol ratio, total CaO:AszOa is 4: which is the same as that of H , but in H the CaO and As205 are in combination. The per cent As205in each sample, F and H , is the same, but the toxicity of the former to the locust (Table 11)is much greater than that of the latter. This would suggest a modification in the manufacture of calcium arsenate, since it is quite evident that a compound containing the same percentage of arsenic as the more basic commercial products can be prepared, which will have a much higher toxicity to some insects. Preliminary experiments on plant toxicity with these types of compounds seem to indicate that if the lime and the arsenical are well mixed plant injury does not occur. Cotton plants were used in the tests. The acid arsenates, A to D.do not vary extremely in relative toxicity, probably because the amount of arsenic in solution is more than sufficient to produce death. The ratio of Ass05in body to A S 2 0 5 in feces does not serve as a good criterion for toxicity in these cases. The more basic arsenates, G and H , which are certainly constituents of commercial compounds, show very low relative toxicities. The results using the boll weevil (Table 111) are merely preliminary, since during the season in which the investigation was carried out but few weevils appeared. The check mortalities were quite high. Since it was impossible to collect the small feces the ratio criterion was omitted. The results show a markedly lower toxicity of the basic arsenates when compared with arsenates more acid than Ca3(AsO&. The basic arsenates have uniform toxicity. The samples F and H have practically the same toxicity to the boll weevil, One colloidal arsenical prepared by Smith (Table I, footnote e) showed toxicity to the locust comparable with that of Ca3(As0&.8H20. The average longevity from one test of rather low dosage, 0.2 gram, was 39.1 * 1.1 hours. Summary
Average longevity and the ratio of As206 in the body to A s 2 0 in ~ the feces are both satisfactory criteria for toxicity of arsenicals. I n the case of the locust and probably other gross feeding insects, the toxicity of calcium arsenates decreases with increase in the mol ratio CaO:AsZOs in combination. It is not materially affected by Ca(OH)2 in the presence of Cas(AsO~)z.HzO. In the case of the boll weevil the ‘basic arsenates have a constant toxicity. The acid arsenates are much more toxic than the basic arsenates. Acknowledgment
The writers wish to thank B. R. Coad of this laboratory for his assistance in this work. @
J. Agr. Research, 26, 192 (1923).
Carnegie Fund for Science Increased-The Endowment Fund of the Carnegie Institution of Washington has been increased t o $27,000,000 by an appropriation of $5,737,000 by the Carnegie Corporation of New York. The money will be paid in five annual instalments of $1,000,000 beginning with 1926, and $5,000,000 will go to the endowment fund proper. The approved budget contemplates scientific work in many important lines.
