590

SECONDARY RESULTS OF ELECTROLYSIS.

[288. of the tube becomes positively electric by contact with the glass, and its positive electricity tends to move in the same direction as the positive electricity of the current; but since the particle of water cannot instantaneously part with its electricity, it is carried forward in the direction of the positive current: and these motions can only occur in imperfect conductors, which retain their charge for a sensible time. If a foreign substance, such as a grain of starch, be suspended in the water, it becomes negatively electric by simple contact with the water, and independently of the current from the machine,-water having been shown, by Faraday and others, to become positively electrified by friction with every substance hitherto tried; and when two bodies become electric by contact, the electricity which each acquires is the same as that developed by rubbing them together. If a conducting liquid be added to the water, these conditions of the development of electricity by contact are altered, and the motion of the particles is arrested.

Oil of turpentin, on the contrary, becomes negative by friction and by contact with all substances hitherto tried, except sulphur, and consequently the direction of the movements is reversed. (Quincke, Ann. Chim. Phys. 1861 [3], lxii. 381, and [3], lxiii. 479.)

(289) Secondary Results of Electrolysis.-The explanation already given of the mode in which the oxysalts are electrolysed was happily applied by Daniell to the elucidation of the origin of the voltaic power, in a combination contrived by Becquerel (262), which presents many interesting peculiarities. If a porous tube filled with nitric acid be plunged into a vessel containing a solution of potash, and the wires of a galvanometer, armed with platinum plates, be plunged one into the nitric acid, and the other into the alkaline solution, a current will circulate; oxygen will be emitted from the plate immersed in the potash, and nitrous acid, owing to the absorption of hydrogen by the nitric acid, will be formed around the other plate, whilst potassic nitrate is slowly produced by transudation of the two liquids through the pores of the diaphragm. By connecting several of these cells together in succession, upon the principle of the ordinary battery, the power may be considerably augmented. The decomposition which appears to occur is represented by the following symbols, in which H,NO, indicates the nitric acid, and K,HO the potassic hydrate : the position of the brackets above the symbols indicates the arrangement before the current is established, whilst after its

289.]

SECONDARY VOLTAIC DECOMPOSITIONS.

591

passage, the arrangement is supposed to be that indicated by the brackets beneath :

H,NO, H,NO, | K,HO K,HO.

It is particularly to be observed that no development of oxygen or of hydrogen occurs upon the platinum plates until the two plates are united by a conducting wire, and it ceases as soon as the conducting communication between the plates is interrupted: in the latter case the polar arrangement of the particles is interfered with, although the reaction of the caustic potash upon the nitric acid continues. The secondary action of the nitric acid on the hydrogen which is set free is necessary to the development of the current. If sulphuric acid be substituted for the nitric, the hydrogen is not absorbed, and no current is obtained, probably because it is neutralized by the counter-current which the accumulation of the hydrogen upon the platinum plate tends to produce (264).

The secondary actions of the voltaic current are often of great importance; they require to be carefully distinguished from its primary effects. Secondary results are, in some instances, produced by the action of the liberated components of the electrolyte upon the materials employed as electrodes: for example, if a slip of copper be substituted for one of platinum, as the zincode of the battery, and be immersed in diluted sulphuric acid, cupric sulphate will be formed by the combination of the copper with the disengaged sulphion. At other times, the secondary results are manifested by the reaction of the ion upon the liquid in which the electrolyte is dissolved, as when the potassium or sodium, set free at the platinode in an aqueous solution of its salts, liberates hydrogen by its action upon the water; K2+2 HHO=H2+2 KHO. In the cases just cited, the chemical attractions of the disengaged ions are very intense, and the secondary action is exactly proportioned to the primary; so that it may be employed as a measure of the current: but when the tendency to combination is more feeble, the proportion of these secondary actions to the primary one is greatly influenced by the extent of surface exposed by the electrode to the liquid, and by the energy of the current, and consequent quantity of the ion disengaged at once. Generally, the slower the action, and the larger the surface of the electrode, the more uniform and complete is the secondary action. The results are well exemplified

592

METALLOCHROMES.

[289. by Bunsen's researches on the isolation of the more oxidizable metals by the voltaic current. If a thin platinum wire be used as the platinode in a solution of chromic chloride, to convey the current from 4 or 5 cells of the nitric-acid battery, metallic chromium may be obtained without difficulty: but if a plate of platinum be employed, chromic oxide, mixed with a certain amount of hydrogen, is liberated; in the latter case the metal has time to decompose the water before fresh particles of chromium are deposited upon its surface.

In consequence of these secondary actions, the same element may sometimes appear at one electrode, sometimes at the other, as is seen in the case of nitrogen: if, for instance, a solution of ammonic sulphate be submitted to electrolysis, it yields ammonia and hydrogen at the platinode, and a mixture of nitrogen with oxygen is set free at the zincode. The nitrogen in this case is liberated as a secondary result of the combination of a portion of the oxygen with the hydrogen of the ammonia. If ammonic nitrate be substituted for the sulphate, nitrogen appears among the gaseous products at both electrodes, the nitric acid being deprived of its oxygen by the hydrogen evolved at the platinode, and the ammonia of its hydrogen by the oxygen set free at the zincode.

If a solution of plumbic acetate be employed as the electrolyte, the acetic acid undergoes partial decomposition from the action of the oxygen upon it at the moment of its liberation at the zincode, but at the same time a portion of the oxygen also enters into combination with some of the plumbic oxide contained in the liquid, and, as Warrington proved, a deposit of plumbic dioxide (PbO2) is produced. Nobili, who first observed this phenomenon, found that if a polished steel plate be employed in such a solution as the zincode to the battery (4 or 6 cells of Grove's may be employed), the deposit assumes the form of a thin film, which exhibits the iridescent tints of Newton's scale,-the tints varying according to the thickness of the film produced. Other experimentalists have modified the patterns which may be obtained by these metallochromes, which have been applied by Becquerel even to the imitation of the tints of flowers; and by varying the strength of the battery and of the solutions employed, he has succeeded in producing some effects of great delicacy and beauty. Salts of manganese or of bismuth may be substituted for those of lead, with similar results.

Many of these secondary actions are very interesting: Kolbe has devoted particular attention to the effects of oxygen when

290.]

NASCENT STATE OF BODIES.

593

liberated during electrolysis (Mem. Chem. Soc. 1846, iii. 285, and Q. J. Chem. Soc. 1849, ii. 157). Hydrochloric acid, especially when previously mixed with sulphuric acid, is in this manner partially converted around the zincode into chloric and perchloric acids; and in an acid solution of potassic chloride, potassic chlorate and perchlorate are formed. Potassic cyanide in solution, when subjected to the voltaic current, is in like manner converted into the cyanate. A concentrated solution of salammoniac (H,NCI) evolves hydrogen at the platinode, but the chlorine, instead of being liberated at the zincode, acts upon the sal-ammoniac, and forms oily drops of the so-called chloride of nitrogen, which explode when touched by the opposite electrode. Smee has shown that by means of the voltaic current the ferrocyanide may be converted into the ferricyanide of potassium. Kolbe has, further, ascertained the effect of the liberated oxygen upon various organic compounds, and by submitting potassic valerate (KC,H,O) to electrolysis he decomposed the radicle of valeric acid (C,H,O) which it contains, and succeeded in obtaining from it a new substance valyl (CH)2, (or more properly tetryl); a new ether, (CHO) tetrylic ether, and a hydrocarbon (CH), apparently identical with oil-gas: and by a similar process from acetic acid (HC,H,O2) he obtained methyl (CH3)2, the homologue of tetryl. Particular interest is attached to these researches, owing to the circumstance that in each case the compounds obtained by the electrolysis belong to a series related to an alcohol different from that which was submitted to decomposition. The valerates thus yield an ether of the tetrylic series: and the acetates, which are derivatives of wine-alcohol, furnish a hydrocarbon which belongs to the wood-spirit series.

(290) Nascent State of Bodies.-It is obvious, from the powerful effect which oxygen produces at the moment of its liberation from compounds during electrolytic decomposition, that such oxygen must be in a condition very different from that in which it exists when once it has assumed the gaseous form. Oxygen is not insoluble in water, and it is therefore possible to bring it in small quantities at a time into chemical contact with salts or other bodies which water may hold in solution. Oxygen gas may, however, be passed for an unlimited time through a solution of potassic chloride without effecting the conversion of any portion of the chloride into chlorate, or into perchlorate of potassium; and yet, as has been mentioned in the foregoing paragraph, this change is easily effected by oxygen as it escapes during the electrolysis of an acidulated solution of potassic chloride.

594

NASCENT STATE OF BODIES.

[290. But it is not necessary that oxygen should be liberated by the agency of the voltaic battery in order that it should acquire this increase of activity. If hydrated nickelous or cobaltous oxide be suspended in a solution of caustic potash, it will undergo no change when subjected to a current of oxygen gas; but if a current of chlorine be substituted for the oxygen, the whole of the metallic oxide will be converted into a brown sesquioxide; this change arises from the action of the chlorine upon the potash, during which, potassic chloride is formed, whilst oxygen is set free, and at the moment of its liberation attaches itself to the nickelous or

cobaltous oxide, 2KHO+Cl2+2(NiO,H,O)=2 KCl + Ni2O,,3 H2O. Other substances besides oxygen exhibit this peculiarity, and chemists have long recognized the fact that bodies, when in this nascent state—that is to say, when in the act of liberation from other substances-display more energetic attractions than they show when once obtained in the isolated form :-For example, cyanogen and chlorine do not enter directly into combination; 'but if cyanogen at the instant that it is set free from another compound, be presented to chlorine, the two bodies combine; so that if moist mercuric cyanide be decomposed by means of chlorine, chloride of cyanogen may be obtained: the chlorine removes the mercury step by step, and the cyanogen at the moment of its liberation enters into combination with another portion of chlorine. In a similar manner, sulphur when set free from an alkaline persulphide in the midst of a solution of hydrochloric acid, combines with hydrogen, and forms persulphide of hydrogen, K2S2+2 HCl=H2S, +2 KCl, the chlorine taking the potassium, whilst the sulphur and the hydrogen, both in the nascent state, unite to form a new compound, although their chemical attraction is so slight that this compound separates spontaneously into sulphuretted hydrogen and free sulphur. The process of double decomposition is particularly applicable in cases where the mutual attraction of the bodies which it is desired to obtain in combination is comparatively feeble. It is not impossible that this superior chemical activity of bodies in the nascent state may arise from the fact that their particles are individually electrified at the moment of their separation from a previous state of combination; and that in this condition they may exert upon the particles of dissimilar contiguous matter, a force of induction which may be the agent that determines their chemical combination if by a process of double decomposition the particles of both compounds were oppositely electrified, combination might be expected to be proportionately facilitated :-For instance, if a solu