December, 1924
I N D U S T R I A L A N D ENGINEERING CHEJfIXTRY
ment. The mechanicitl properties (Table IV), too, confirmed this circumstance, except for the fact that heat treatment improved the percentage of elongation of the chill-cast specimens. The sand-cast alloy containing 0.54 per cent of magnesium (hlelt 2337) was much like Melt 2339 except for a somewhat greater quantity of compounds. Some globular Mg,Si was found in the unsegregated area, and more in the form of skeletons in the segregated areas. It was not possible to identify MgZSi in the chill-cast specimen. Quenching (and aging) and annealing (furnace cooling) effected the disappearance of the MgnSi found in this alloy as cast, but the gray needles and skeletons containing iron were not changed. With the exception of this melt, the metallography of the various alloys after heat treatment was the same as that in the alloys as cast, the excess of magnesium contributing to the insolubility of the NfgzSi a t the quenching temperature. The sand-cast alloy having 1.08 per cent of magnesium (Melt 2340) contained principally iron-bearing needles, considerable lLIgzSi as globules and some as skeletons, and some iron-bearing skeletons. (Fig. 8) There were several clumps of very small globules of MgzSi about R nucleus of an ironbearing particle or particles. Besides the iron-bearing needles, the segregated area showed many skeletons of Mg&. (Figs. 11 and 12) Iron-bearing skeletons, of the unidirectional type depicted in Fig. 13,were found only in unsegregated areas. Figs. 14 to 18, inclusive, are of the heat-treated alloy. In Figs. 14 and 15are represented the structure a t and adjacent to a pipe. Segregation caused the separation of what is evidently primary FeA13. A poly-axial, iron-bearing skeleton is to be observed in Fig. 16. This should be compared to that shown in Fig. 13. Undissolved Mg,Si was present in both the quenched and the annealed specimens. (Figs. 17 and 18) Except in the case of the chill-cast material, in which the percentage of elongation was improved, heat treatment produced practically no change in tensile properties and none in hardness except in the case of the annealed material; whereas the only observed structural alteration was a tendency toward coagulation in the particles of MgzSi. The nietallography of the cast alloys containing 3.08 and 4 96 per cent of magnesium (Melts 2327 and 2326) was similar to that of the 1.08 per cent alloy, except that no iron-bearing skeletons were found. Both were characterized by the presence of a plentitude of Fe& (?) needles and about onethird the quantity in skeletons of MgzSi, the former often cutting across the latter, testifying as t o their higher melting point. According to the investigations of Hanson and Gayler the melting point of MgzSi is 1076’ F. A peculiar skeletonlike crybtallite containing iron (Fig. 19) was found in the annealed specimen only. Drossy areas were considerably more prominent in these high-magnesium alloys, especially in the 5 per cent, than in those of low magnesium content. I n order to ascertain the identity of the gray, iron-bearing particles mzntioned above, recourse was had to etching the spccimeris in the nitric acid quench and in 2 per cent aqupous hydrofluoric acid. Long-continued etching failed to reveal reaction .ims or staining which might have indicated the presence of X constituent. All these gray needles and skeletons were therefore thought to be Fe&, with the exception that in Ihe alloy containing 0.27 per cent of magnesium the X constituent might have been present. It is suggested that the presence of magnesium in aluminium alloys containing iron and silicon materiallgr alters the equilibrium diagram given for the aluminium-iron-silicon series by the British investigators in the already cited Eleventh Report. It appears that magnesium has a greater affinity for silicon than iron possesses,with the result that the formation of the X constituent may be entirely suppressed when the content of magnesium is sufficiently great to combine wit11 all the silicon as MgzSi.
1249
Sodium Fluosilicate as an Insecticide’ By S. Marcovitch AGRICITLTURAL EXPERIMENT STATION, KNOXVILLE, TENN.
MONG the many different chemicals tried out this past A season against the Mexican bean beetle and the cotton boll weevil, sodium fluosilicate appears to be the most promising. The efficiency of sodium fluoride in killing roaches and chicken lice is now well established. It cannot be used on plants, however, because of its solubility and consequent “burning” of the leaves. A study of other less soluble fluorine compounds revealed several-such as sodium fluosilicate, calcium fluosilicate, and cryolite-that the plant will tolerate and that retain the efficiency of sodium fluoride. The value of sodium fluosilicate as an insecticide is due to the fact that it is both a contact and stomach poison. Shafer2 has determined that when a roach walks over powdered sodium fluoride a little of the powder adheres t o the lower part of the body, antennae, and tarsi of the feet, and dissolves in the exudations of the integument. This seems to cause some irritation and uneasiness; the insect Soon begins to clean the moistened powder from the body by licking it. I n doing this enough of the poison may be brought into the mouth and swallowed, to kill after a period varying in from five to ten days.
Other insects, such as Mexican bean beetles, also have the habit of cleaning themselves and by putting their feet in their mouths become very easy to kill. For this reason the sodium fluosilicate is more effective against the adult beetles than the larvae, which do not have these habits. In the field trials sodium fluosilicate was mixed with nine parts of hydrated lime by volume and used as a dust. For the best results, the dusting should be started as soon as the beetles appear and before egg-laying gets under way. Four or five applications a t intervals of a meek or ten days were sufficient to give excellent protection and showed a net return of $187.60 per acre. Other insects against which sodium fluosilicate mixed with lime was used successfully are the Colorado potato beetle, the potato flea beetle, bean leaf beetle, and tobacco hornworm. When used pure, under cages, it was an efficient insecticide against the cotton boll weevil. In all the cage tests conducted the weevils were killed in from 5 to 24 hours. It was also observed that the weevils could be killed entirely by contact with the powder. T o make sure that the weevils were killed by contact alone, they were placed on a bean plant dusted with sodium fluosilicate. After crawling over the bean plant (which weevils do not eat) 50 per cent of the weevils were dead in 6 hours; the rest were found dead the next morning. I n the control cage, untreated, all were alive. The advantages of sodium fluosilicate over the arsenicals as an insecticide are (1) it is cheaper, (2) it acts as a contact as well as a stomach poison, (3) it kills more rapidly, (4) it is not so poisonous to people, and ( 5 ) its effectiveness against a wide range of insects, such as chicken lice, roaches, tobacco hornworms, potato beetles, potato flea beetles, Mexican bean beetles, and cotton boll weevils. The disadvantage of sodium fluosilicate as obtained on the market today is its density. A pound will occupy about 30 cubic inches. For dusting purposes best results are obtained when a material occupies in the neighborhood of 80 cubic inches, in order to cover as large a surface as possible. The factor of density has been solved for calcium arsenate, and there is hope that with further research a sodium fluosilicate that will be suitable for dusting will be obtained. More detailed results will be given in a forthcoming bulletin. 1
2
Received October 11, 1924 Mich Agr. Expt Sta,, Tech Bull. 21.
