CHEMICAL SCIENCE. 241 



old, with a saturated solution of arsenious acids, in every trial, after two 

 doses at intervals of three days, the plants died within the week. The same 

 occurred with Scotch kale, the only other plant subjected to the experiment. 

 On testing the dead plants arsenic was detected only in the portion of the 

 stem close to the roots, and which showed in its darkened color the marks of 

 disease. In no case was any of the poison found in the leaves, or in the 

 stem at more than five inches above the ground. Professor Davy also 

 startled the English agriculturists and medical jurists by calling attention to 

 the fact that arsenic exists in the commercial superphosphate of lime, at least 

 in certain kinds, coming from the iron-pyrites used in the manufacture of the 

 sulphuric acid employed in the production of the superphosphate, which 

 arsenic, if plants may accumulate it in their tissues, would be conveyed to 

 the flesh of animals fed with turnips manured with such superphosphate, 

 and so conveyed to the human system, if not in quantity sufficient to poi- 

 son, yet enough to account for the presence of arsenic in cases of death from 

 supposed poisoning. Mr. Ogston now considers the question as to how much 

 arsenic an agricultural crop (say of turnips) can obtain from an ordinary 

 dressing of the superphosphate so prepared. "Take a very bad sample of 

 pyrites said to contain .30 per cent of arsenic, and consider, as is the case, that 

 in the manufacture of oil of vitriol one-half of this is stopped by condensa- 

 tion in the flues; .15 per cent will remain in relation to the pyrites, or about 

 .10 in relation to the manufactured oil of vitriol. Now, suppose the super- 

 phosphate made from this acid to contain twenty per cent, of it as a constit- 

 uent, and that three hundredweight are used as a dressing per acre, there will 

 be added to this acre .07 of a pound of arsenic, and this is to be distributed 

 among from twenty to twenty-five tons of roots, giving a percentage infin- 

 itely small, and in my opinion relieving us from the necessity of the smallest 

 anxiety on the subject. 



ON FERMENTED BREAD. 



It is well known to our readers that, some two years ago, a new plan of 

 preparing bread was devised by Dr. Dauglesh, of Scotland; 1 in which, in the 

 place of generating carbonic acid within the substance of the dough by fer- 

 mentation, water charged with carbonic acid (common "soda water ") was 

 mixed under pressure with the flour, effecting thereby a raising of the bread 

 by mechanical means, imparting to it a most perfect vesicular structure, 

 and leaving the constituents of the flour wholly unchanged. An objection 

 having, however, been made by some medical authorities to the process 

 (which has been experimentally introduced in Great Britain), that the con- 

 stituents of flour, especially the starch, are not fit for human food until they 

 have been subjected to fermentative action, Dr. Dauglesh, in a late number 

 of the London Medical Times and Gazette, combats the objection in the follow- 

 ing article, which our readers will find replete with valuable and interesting 

 infownation. He says : 



In order to dispose of the assertion that starch requires to be prepared by 

 the fermentive changes to render it fit for human food, it is but necessary to 

 remark, that the proportion which the inhabitants of the earth who thus 

 prepare their starchy food bear to those who do not is quite insignificant. 

 Indeed, it would appear that the practice of fermenting the flour or meal of 



1 See Annual of Scientific Discovery for 1359, p. 275. 



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