INJURY BY DISINFECTANTS TO SEEDS AND ROOTS. 27 



Volume for volume, the hydrochloric and nitric acids used did not 

 seem to differ greatly in their effect on the pine seedlings or weeds, 

 the hydrochloric acid appearing rather the more dangerous. The 

 tests offer little opportunity for direct comparison. As with sul- 

 phuric acid, pines were less injured than weeds, and the grasses pres- 

 ent seemed more resistant than the dicotyledons. The difference 

 in the effect on jack pine, grasses, and Mollugo verticillata shows 

 especially well in series 512 and 519, in whose checks Mollugo was 

 the most common weed. 



The tests show clearly the low toxicity of these acids in this soil 

 as compared with sulphuric acid, volume for volume. Comparison 

 of plats C and J of series 501 with plats B, D, and H in the same 

 series indicates that sulphuric acid is three or more times as danger- 

 ous to both pines and weeds as nitric acid and much more dan- 

 gerous than hydrochloric acid. In series 512, sulphuric acid seems 

 two or three times as active against the pines as the other two acids, 

 while the disparity in the action on weeds appears still greater. In 

 series 516, results in plats A and D treated at the same time indicate 

 that sulphuric and hydrochloric acids are equally toxic to the weeds 

 when the amount of hydrochloric acid used is three times the amount 

 of sulphuric. In series 518, plats P and Q, 0.375 ounce of hydro- 

 chloric acid per square foot appeared considerably more active 

 against weeds than 0.125 ounce of sulphuric acid used on the adja- 

 cent plat. Weight for weight, the disparity between the two acids 

 is much less. While the strengths of the acids used were not deter- 

 mined, a statement of the amounts used indicating relative concen- 

 trations of ionic hydrogen would have further decreased and might 

 have entirely obliterated the apparent disparity in action between 

 the three acids, as was found by Kahlenberg, 1 True, 2 and Heald 3 in 

 their work with these acids in water culture. For instance, using 

 for comparison sulphuric acid containing 90 per cent H 2 S0 4 and mak- 

 ing no allowance for impurities, nitric acid containing 60 per cent 

 HN0 3 would contain, volume for volume, but 43 per cent as much 

 ionic hydrogen, and 30 per cent hydrochloric acid but 31 per cent 

 as much, assuming equally complete dissociation in the dilute solu- 

 tions of the three acids. 



TOXIC SALTS. 



Copper sulphate, tested only twice, gave rather contradictory 

 results. In series 518, plat G (Table VI), 0.188 ounce per square foot 

 17 days before sowing caused little or no injury to pines and consid- 



1 Kahlenberg, Louis, and True, R. H. On the toxic action of dissolved salts and their electrolytic disso- 

 ciation; In Bot. Gaz., v. 22, no. 2, p. 81-124, 1896. 



2 True, R. H. The toxic action of a series of acids and of their sodium salts on Lupinus albus. In Amer. 

 Jour. Sci., ser. 4, v. 9, no. 51, p. 183-192, 1900. 



8 Heald, F. D. On the toxic effect of dilute solutions of acids and salts upon plants. In Bot. Gaz., v. 

 22, no. 2, 1896, p. 130. 



