34 NUTRITION OF VEGETABLES. 



of piitrctaction; &c., have the same effect. Hence we may 



infer, that all those matters, which are injurious to animals, 



seitsibly affect vegetables likewise. 



Carbpuic acid \\q cannot therefore lay much stress on Saussure's expe- 

 not useful, ... 



nments to show the utility of carbonic acid in vegetation, 



particularly when we recollect an experiment of Priestley's, 

 which proved, that an atmosphere with an ei^^hth part of 

 but injurums carbonic acid was sufficient to kill two plants of mint, though 

 proportion ^'^^ ^^'^ Small quantity of acid was ia contact with a large sur- 

 face of water. 

 Seeds germi- Having found by experiment, that seeds germinate very 

 ide of lead ^^^^^ '" oxides of lead, which are known to be greedy of car- 

 bonic acid, I conceived, that these might contribute to elu- 

 cidate the question respecting the utility of carbonic acid in" 

 vegetation. In consequence I moistened with distilled wa- 

 butnotif re- ter some recently prepared oxide of lead in the lirst stage of 



ccntiv ofC" • 



pared oxidation. This mixture I introduced speedily into a flint 



glass bottle : and though the disagreeable and as it were al- 

 kaline smell that arose from it, led me to doubt the success 

 of my experiment, t sowed some mustard seed in this oxide, 

 and included in ajjfl corked the bottle tight. As I foresaw, no germination 

 took place : but what I was far from expecting, and to my 

 The lead partly great surprise, part of the oxide of lead in the water was re- 

 re uce , duced by the seeds, each of which was enveloped by a shining 

 coat of metallic lead. This appeared to me to be very pro- 

 bably owing to a production of water by the union of the 

 oxigen of the oxide with the large quantity of hidrogen, that 

 is condensed in this oily seed, which after the reduction was 

 more or less carbonized. 

 If tlie oxide ^^ ^^^ oxide of lead be left exposed to the air for some 

 have been ex- time after it is made, and then put into a bottle with water 

 siiT*the°ceds ^"^^ seeds, no reduction of the metal will be effected, but 

 grow. germination will take place. 

 Oxide of lead These experiments show the extreme facility, with which 



easily reduced the oxides of lead are reduced, and the obstacle that car- 

 unl-ss carbonic , . . , ^ ^i • j i- 



aci»l prevent it, bomc acid opposes to this reduction. 



As these first attempts did not afford me the result I 



sought, I availed myself of an old experiment of Huyghens, 



Seeds so'wn in who, in l672, put some earth into a bottle, corked it up, and 



siliceous earth, f^^j^d i^ produce such a quantity of plants, as almost to till 



ties, ' the 



