8o6 THE POPULAR SCIENCE MONTHLY. 



taken for other purposes ; the knowledge of the making of china 

 and of the separation of phosphorus resulted from experiments 

 intended for producing gold. But the principal successes of mod- 

 ern science in general, and of chemistry in particular, were ob- 

 tained in a speculative, inductive way, the only one to be consid- 

 ered as actually scientific. With positive surety the astronomer, 

 from the movements of the stars, and from the attracting forces 

 which they thereby manifest, can ascertain the presence of an- 

 other star which has never been observed before. He may 

 prophesy a solar eclipse to the accuracy of a minute, and many 

 years before predict the return of a comet. In a similar way exact 

 chemical knowledge often enables us to foretell the formation of 

 certain compounds hitherto unknown, and to define the properties 

 they may be expected to have. It was in this way that, the com- 

 position and chemical structure or arrangement of atoms in the 

 molecule of conine and conhydrine having been explored, their 

 preparation was likewise effected, the operators being guided by 

 logical inferences. This scientific way of proceeding proved suc- 

 cessful in numerous cases, and led to some surprising results in 

 the course of the last year. 



Not many years ago what was known regarding the source 

 from which common plants draw their food consisted in the rec- 

 ognized fact that carbonic acid and water, both abundant in air 

 and fertile soil, are taken up by the roots, converted into sugar by 

 an unknown process, the sugar afterward being transformed into 

 cellulose, the matter chiefly constituting the body of the plant, and 

 into starch. It was also known that oxygen was set free in the 

 course of these changes. In 1870 Baeyer promulgated a theory, 

 explaining how assimilation of the mentioned substances might 

 be effected. He demonstrated the possibility of " formaldehyde " 

 being produced from carbonic acid and water, which is only pos- 

 sible, if — as is the case — oxygen is liberated. All plants in day- 

 light exhale oxygen and absorb carbonic acid. Formaldehyde, a 

 gaseous compound, is, as aldehydes in general are, very liable to 

 condense to solid compounds by accumulating a greater number 

 of atoms into one molecule. Baeyer expressed his belief that 

 sugar, the composition of which agrees with that of formaldehyde 

 multiplied by six, is the product of such a condensation.* 



The first signs that sugar might result from such a condensa- 

 tion, when conducted in the proper way, were observed by Butle- 

 row, but since he claimed to have prepared a sugar-like com- 

 pound from formaldehyde, all the experiments undertaken to the 



* The chemical changes in question are represented by the equations : 

 Carbonic acid and water = formaldehyde and oxygen 



CO, + H„0 = CH a O + O a 



Six formaldehydes, 6CH a O = CgHiaOg, grape-sugar. 



