334 T-he Philippine Journal of Science 1920 
Sterling’s observation would therefore seem to support the 
conclusion brought forward here; that is, that a spray of Bor- 
deaux 4-4-50 mixture, because of its more lasting bactericidal 
properties in addition to its immediate killing capacity, is more 
valuable than a disinfectant which is washed off by the first 
rain or is evaporated soon after application. 
In spraying tests in the field it had been suggested that the 
so-called neutral Bordeaux mixture might prove of greater value 
than Bordeaux 4-4-50 mixture. The term neutral Bordeaux 
mixture was used for a mixture in which the amount of lime 
added was just sufficient to precipitate all of the copper, with no 
excess. The reasoning followed in this suggestion apparently 
was that with an excess of lime, soluble copper salts would be 
available only after long weathering; with just the proper 
amount of lime to precipitate the copper entirely, with no ex- 
cess, it seemed to follow that the soluble copper salts would be 
liberated more freely. Tests in the field with such a neutral 
Bordeaux mixture showed no advantage whatsoever over the Bor- 
deaux 4-4-50 mixture; on the contrary, in the two-year trials 
in which the two mixtures were compared, a very slight ad- 
vantage lay with the Bordeaux 4-4-50 mixture. Tests to com- 
pare the two mixtures by Anderson and McClintic’s method were 
therefore made. The results are best shown in Table 9. 
Table 9. — Results of exposures with 3-day-old culture of Pseudomonas 
citri in dilutions of neutral Bordeaux mixture . a 
[Date of test, August 13, 1920 ; date of observation, August 16, 1920.] 
Exposure. 
Dilution expressed in percentage. 
10. 
20. 
30. 
40. 
50. 
60. 
70. 
<80. 
90. 
100. 
Min. sec. 
2 30 
b + 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
•>+ 
5 00 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
7 30 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
10 00 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
12 30 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
15 00 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
b + 
b + 
a The neutral Bordeaux mixture was made up with autoclaved tap water to avoid con- 
tamination ; otherwise the preparation was entirely similar to the mixtures as prepared in the 
field. The neutral point was determined as nearly as possible by litmus paper tests. 
b Exposure tested for P. citri, August 16; positive, August 18. 
Tests with this mixture were repeated seven times; four of 
the tests resulted entirely uniformly with no killing of the canker 
bacteria whatsoever. The other three showed killing at the 
