118 Answers to Queries, 
ask whence it is that the plant gets the supply of energy it uses for 
chemical construction. It has been proved that the green plant 
uses the energy of sunlight. Exposed to air, it gets carbon 
dioxide, light, water, and ammonia from the soil. The plant 
builds them up again, giving off oxygen. Vaal 
361.—Plants.—Green vegetation gives out oxygen, as chloro- 
phyll has the property of decomposing carbonic acid during 
sunlight, but not in darkness. This giving out of oxygen and 
absorption of carbonic acid must be carefully distinguished from 
the process of respiration of plants, which only goes on to a. very 
slight extent, and consists in taking in oxygen from the air and 
probably giving out carbonic acid. This process of respiration 
goes on continually both in light and darkness as it does with 
animals, but during sunlight it is largely masked by the process of 
nutrition, concerning which W. asks, and which consists in the 
plant taking in carbonic acid and giving out oxygen. This process 
is suspended during darkness, when the exhalation of carbonic acid 
is more readily observed than it is during the day-time. J. W. G. 
363.—Explosion of Potassium.—In Watt’s ‘“ Dictionary of 
Chemistry ” it is stated :—‘‘The Potassium obtained by this process 
is not pure, but always contaminated with compounds containing 
carbon and oxygen. To remove these, it must be distilled a 
second time in an iron retort, and this precaution is essential, as if 
the crude potassium is exposed to the air, and even if it is pre- 
served under naphtha, a black detonating compound is quickly 
formed, which explodes violently on the slightest friction.” 
B.. On iB: 
364.—Divergent Series.—According to definition, a divergent 
series 1s one whose sum does oft approach a finite and unique 
limit as the number of terms added up is continually increased, so 
that the ‘sum or value” spoken of by F. 5S. S. has no existence. 
In the case of the first series named (viz.. :—2 + 4—8 + 16...) 
the sum of # terms is [1— (—2)" ] + 3. When ~# is made infi- 
nite, this becomes infinite, and is positive or negative according as 
mis odd or even. It is only when a series is convergent that we 
can speak of its having a sum, and this can never happen when 
the terms keep on increasing. 
The series mentioned in the second query are known as 
figurate numbers of the third and fourth orders. ‘The various 
orders are as follows :— 
Ist order ome TART, Ty 62 Sie eee 
2nd order ae ie A PRR eh 2 
3rd order ise Te 4.35 0, TC aipeeeee 
4th order ap i, A, LO, 20, “anaes 
5th order ic My 5eol5) 355: 7 Onoheies 
