EXPERIMENT STATION BULLETINS. 475 



Before figuring tlic rates given in Table VII, all gas-volumes were 

 reduced to 0° C, and 760 m. m. mercury pressure. Since all tests were 

 not run for equal x^eriods of time, it was necessary to figure results to 

 some certain period — a ten-hour period was used. Results of experi- 

 ments with gasoline-vapor are those ol)tained through estimating the 

 actual amount of oxygen present at the beginning and end of each test. 

 Where two or three determinations were made, the value given under any 

 test number in the table is the value which came nearest the average. As 

 has already been mentioned, however, all determinations (by both meth- 

 ods) led to the same general conclusion already stated. 



In this connection, it occurred to the author that a good opportunity 

 had presented itself for testing the effect of lime-sulphur, itself, upon the 

 permeability of a wax membrane to oxygen. Accordingly two series of 

 tests, results of which are given under Nos. 7 and 8 of Table VII, were 

 carried out, using bees wax and shellac membranes. The membranes 

 were formed by dipping thin India linen in melted beeswax, and in 

 melted shellac, until membranes of the desired Ihickness were obtained. 

 After the tests with a dry membrane had been carried out, the prepara- 

 tion dish (over which the membrane was fastened as a cover) was in- 

 verted and shaken until the lime sulphur in the dish had thoroughly 

 wet the surface of the membrane inside the dish. Before test No, 2 

 of Exp, 8 was tried, the preparation dish was only shaken. It was 

 again thoroughly shaken, before test No. ?r, and before the fourth test 

 the dish was inverted — the lime-sulphur solution being left in contact 

 with the shellac membrane, thus, for 25 minutes. In that time, the 

 solution had ''taken hold'' and thoroughly wet the membrane. Note 

 the decline in Ihe rate of oxygen transfer. Both sets of tests showed 

 that much less oxygen was absorbed (i, e. passed through the membrane) 

 after the membrane-surface, inside the preparation dish, had been wet 

 with the solution. That is, the lime-sulphur solution rendered the wax 

 membranes decidedly less permeable to oxygen — less able to transmit 

 oxygen. There seems to be no reason why lime-sulphur* would not have 

 the same effect upon the wax covering of a scale insect, such as that of 

 the San Jose scale. 



A few experiments had been made a long while ago with living grass- 

 hoppers [Melanoplus) in air containing very strong fumes of osmic acid. 

 These insects were darkened, and were rendered clumsy in their move- 

 ments, but they lived for many hours in the fumes of the acid. It seemed 

 a wonder that they could thus withstand the fumes — and that the fumes 

 did not penetrate. In addition to the membrane-experiments just re- 

 cited, therefore, one set of tests was carried out to determine the rate at 

 which oxygen from air could pass through a lecithin-lard membrane 

 before and after the membrane had been exposed to strong osmic acid 

 fumes. Oxygen passed through the membrane at the rate of 1.3 c. c. 

 per hour before treatment with the fumes. The membrane was treated 

 (from one side) with the fumes for over three hours. It was then aired 

 over night, and on the next day, in the three tests made, the darkened 

 membrane did not transmit oxygen at a greater rate than 0.2 c. c. per 

 hour — i. e. the rate was about six times slower than before the treatment. 

 The lecithin-lard membrane was penetrated by the fumes but slowly. 



♦Some other scalcclde properties of lime-sulphur are given in Tech. Bull. 11. 



