ATO 



AUG 



of one atom of each component, but 

 are often in highei ratio, as 1 to 2, 3, 

 4, 5, 6, 7, or 2 to 3, 5, 7, &c. Those 

 are, for the most part, less permanent 

 than the simpler compounds. 



The atomic weight is not only fixed 

 for the first product of two element- 

 ary bodies, but for all other second- 

 ary, tertiary, or quaternary com- 

 pounds resulting therefrom. Thus, 

 ammonia consists of one atom nitro- 

 gen (14) and three atoms of hydrogen 

 (3), and its equivalent is therefore 17. 

 Bemg a strong alkali, it combines 

 with many substances, and always in 

 the proportion of 17. 



In the above table, the letters in 

 parentheses designate the signs or 

 symbols used in chemistry for the va- 

 rious bodies against which they are 

 set. Whenever any of them are used 

 alone it always means one atom : 

 thus, N, C, H, mean one atom of ni- 

 trogen, carbon, hydrogen. In com- 

 plicated bodies, as oxalic acid, a for- 

 mula is written with the symbols, 

 and numbers set against each to des- 

 ignate the number of atoms, thus : 

 (HO, C.2 O3) ; or, sometimes, (H-|-0, 

 2 C-|-3 O), the parentheses indicating 

 an intimate union ; or one of the 

 components of a complex bodv, thus : 

 (2 C + 3 0) + (Ca + O) + 2 ("H +0) 

 means a compound consisting of ox- 

 alic acid, which is the first term, uni- 

 ted to lime, which is the second, uni- 

 ted to two atoms of water, which is 

 the last term, the whole formula rep- 

 resenting the exact composition of 

 oxalate of lime. Whenever the pa- 

 rentheses enclose a formula, and any 

 figures are placed without it, the fig- 

 ure represents the number of atoms 

 of the compound, thus : (S-|-3 O) is 

 sulphuric acid ; 2 (S-f 3 0) is two at- 

 oms of sulphuric acid ; 3 (S-{-3 0) 

 three atoms, &c. The use of sym- 

 bols greatly reduces the labour of 

 writing and reading chemical pro- 

 cesses. 



ATOMIC THEORY. The theory 

 of Dr. Dalton, that chemical union 

 takes place only in definite atoms. 

 See Alom. 



ATOMIC WEIGHT. The equiva- 

 lent or combining weight. See Alom. 



50 



ATROPIA The poisonous alka- 

 loid of the deadly night-shade. 



ATROPHY. In farriery, a mor- 

 bid wasting and emaciation, attended 

 with a great loss of strength in ani- 

 mals. 



ATTRACTION. In physics, the 

 force which draws bodies together ; 

 it is usually, if not always, of electri- 

 cal origin. Attraction is divided into 

 mechanical, as gravity and cohesion ; 

 and chemical, as affinity ; the first, 

 being the force tending to unite mass- 

 es and similar particles, the latter the 

 force producing chemical union. In 

 chemistry it is so far supposed to be 

 an electrical effect, that one of the 

 atoms or groups of every compound 

 is supposed to be.in an opposite state 

 of electricity from the other, and they 

 are respectively termed the electro- 

 negative and electro-positive ele- 

 ments or components. Acids, oxy- 

 gen, chlorine, are electro-negative 

 bodies ; metallic oxides electro-posi- 

 tive. Chemical attraction acts only 

 at insensible distances, and is assist- 

 ed by heat, solution, and minute di- 

 vision ; it is, indeed, frequently de- 

 stroyed by the hardness and insol- 

 ubility, as well as gaseous form, of 

 bodies. 



AUCHENIA. The region of the 

 neck, in mammals, below the nape. 



AUGER, BORING. An implement 

 for boring into the soil. An auger of 

 the above kind, when made of a large 

 size, and with different pieces to fix 

 on to each other, may be very useful- 

 ly applied to try the nature of the 

 under soil, the discovering springs, 

 and drawing off water from lands, 

 &c. In order to accomplish the first 

 purpose, three augers will be neces- 

 sary : the first of them about liirce 

 feet long, the second six, and the 

 third ten. Their diameters should he 

 near an inch, and their bits large, 

 and capable of bringing up part of 

 the soil they pierce. An iron handle 

 should be fixed crossways to wring it 

 into the earth, from whence the in- 

 strument must be drawn up as often 

 as it has pierced a new depth of about 

 six inches, in order to cleanse the bit 

 and examine the soil. — (Johnson.) 



