196 



ACIDEMETRY ACUPUNCTURE. 



It is to be remarked that tbc gases which are ab- 

 ,-orbed by charcoal in greatest abundance, are those 

 most easily reduced to the liquid state by cold 

 and pressure. For vapours, which differ from 

 gases only in respect of ease of liquefaction, are 

 taken up by charcoal and other porous bodies 

 with the greatest readiness. The power which 

 charcoal has long been known to possess, of absorb- 

 ing odours, is accounted for by its possessing in an 

 eminent degree the property of condensing in its 

 pores, vapours and gases. It renders sulphur 

 waters, for example, sweet, by absorbing the sul- 

 phurated hydrogen gas to which these waters are 

 indebted for their odour. 



A circumstance of great importance, as connected 

 with the manufacture of charcoal and gunpowder, 

 is intimately connected with the present subject. 

 Charcoal permitted to lie together in quantity, is 

 observed to become hot, and if left to itself, to take 

 fire. Many serious fires and accidents have arisen 

 from this cause. The most probable explanation is, 

 that the charcoal condenses within its pores, atmos- 

 pheric air, by which process much heat is developed, 

 which accumulates, by virtue of the non-conducting 

 powers of charcoal for heat, to such an extent as to 

 set the mass on fire. Platinum sponge, or platinum 

 in a finely divided state, possesses extraordinary 

 powers of absorbing gases, particularly oxygen. If 

 the platinum sponge has been purified by long boiling 

 with water, and dried in vacuo over sulphuric acid, 

 and then brought into the air, it absorbs the oxygen 

 of the air with so great rapidity,, and so much beat 

 is evolved, as to make the mass red-hot. Spongy 

 platinum well prepared can absorb 700 times its 

 volume of oxygen. Liquids likewise absorb gases 

 in a manner analogous to the above cases of absorp- 

 tion by solids. The volume of water at 64 Fahr. 

 dissolves 



Carbonic arid gag . . 1-06 times its volume. 



Oxygen gas . . . 0-065 



Nitrogen gas . . . 042 



Atmospheric air . . . 0-050 



In the atmospheric air dissolved by water, the re- 

 lative proportions of its ingredients are different 

 from the proportions in atmospheric air itself; there 

 is more of oxygen. 



The phenomena of the absorption of gases and 

 vapours are generally referred for explanation to a 

 power in bodies analogous to capillary attraction, 

 and the gases are supposed to be condensed on the 

 surfaces lining the pores. The idea of a chemical 

 affinity acting in these cases cannot be admitted ; 

 the gas is not intimately united with the minutest 

 particles of the body in a chemical manner, but has 

 merely attached itself mechanically, in a way it 

 must be confessed as yet peculiar to these cases, to 

 the extensive surface afforded by the state of 

 porosity. The density of the gas in this state must 

 be very great ; in the case of oxygen gas, condensed 

 by platinum sponge, for instance, the oxygen must 

 exist therein in a state approaching, if not amount- 

 ing to, the solid state. 



ACIDIMETRY means the testing of acids 

 with reference to their strength and purity. This 

 is a process of great importance in the chemical 

 arts, and is especially applied to the three mineral 

 acids, sulphuric, muriatic and nitric. The specific 

 gravity of these acids is greater than that of water, 

 and the rate of increase of specific gravity is in 

 their case a precise indication of a corresponding 

 increase in the content in real acid, and tables 

 have been constructed which give at once the 

 content in real acid at different specific gravities. 



The instrument n. u<c by the manufacturers, is a 

 glass hydrometer. The sulphuric acid, or oil of: 

 vitriol of commerce, should have a specific gravity 

 of 1'85, or mark 170 on Twaddel's hydrometer. 

 (See Hydrometer supplement.) The greatest specific 

 gravity of the muriatic acid, or spirit of salt of com- 

 merce, is 1-20. or 40 on Twaddel's instrument; it is 

 more generally sold at 36 on Twaddel, or 1-18 

 specific gravity. Nitric acid or aqua fbrtis can be 

 had of specific gravity 1-54, or 108 on Twaddel; but 

 single aqua fortis in commerce stands only 70 on 

 T\v;uldel. Another and more correct mode of esti- 

 mating the real content in acid of the commerrial 

 articles, is by means of alkalies of known strength 

 or by means of calcareous spar in the case of the 

 muriatic and nitric acids. The larger the quantity 

 of alkali any acid can neutralise, the greater i 

 amount of real acid ; and the greater the amount 

 of calcareous spar, or carbonate of li-ne, dissolved, 

 the stronger the acid subjected to the test. The 

 alkali used is ammonia or carbonate of soda, arid 

 the means of ascertaining the precise limit of 

 neutrality is litmus or turmeric paper. The specific 

 gravity of acetic acid does not afford a sure criterion 

 of its strength, and recourse must be had to the 

 more rigid chemical tests. 



The sulphuric acid of commerce generally con- 

 tains a minute quantity of nitrous acid, a substance 

 which is exceedingly hurtful in many operations in 

 dyeing, but most particularly in the dissolving of 

 indigo. The presence of the nitrous acid in sul- 

 phuric acid is tested by pouring upon the latter in 

 a tube a solution of copperas or sulphate of iron. 

 The impurity is detected by the two striking 

 together a deep red colour after the lapse of a 

 second or two. The muriatic acid of commerce is 

 tested for its content in sulphuric acid, by a solu- 

 tion of muriate of barytes ; a white precipitate is 

 the indication of the impurity. Muriatic acid may 

 further contain sulphurous acid; which is detected 

 by adding to the suspected acid some protochloride 

 of tin, generally called crystals of tin, and then 

 diluting with water ; there is a brown residuum if 

 the acid tested contained sulphurous acid. The 

 nitric acid of commerce is tested for sulphuric acid 

 in the same way as muriatic acid ; and for muriatic 

 acid by a solution of nitrate of silver. 



ACUPUNCTURE, (a) is a medico chirurgical 

 operation which was introduced into Europe more 

 than a century ago, and has for time immemorial 

 been practised in China and Japan. It consists in 

 introducing one or more needles of a particular size 

 and shape, into any diseased part, especially where 

 there is swelling and pain. It has been employed 

 in chronic rheumatisms, and muscular and neuralgic 

 rheumatism, unaccompanied by heat, in sciatica, 

 lumbago, nervous and convulsive affections, sprains, 

 contusions, uterine pains, hiccup, and hysterics. In all 

 cases where a watery fluid is lodged under the cutis, 

 or among the cellular substance, or the fascia of the 

 outer layer of muscles, acupuncture may be employed 

 with advantage. 



There is a species of acupuncture in which the 

 operation is associated with galvanism and electri- 

 city, under the name of the electro, or galvanic 

 puncture, which has in some cases been attended 

 with good effects. 



It is about seventeen years since this practice 

 was revived ; but notwithstanding its acknowledged 

 good effects in numerous cases, it is now again on 

 the wane, and quickly sinking into that obscurity, 

 in which for more than a century it formerly re- 



