that aluminium will replace mercury from a solution of mercuric chloride, without the aid of heat, heaving a solution of aluminium chloride and metallic mercury. The dot and dash dine indicates a solute, and we may have expressed such a state by giving the symbol of ionization : meaning that 66 the elements on either side of it are free to take on any new alliances if such becomes possible. Our sequence then would be :2A1/3Hg: 6C1 - 2A1: 6C1/3Hg, and we should have to understand that 2AI : 6C1 means 2AICI, in solution. The symbol / means added to " and may at times be replaceable by the symbol, as in the mixture of two solutes, say, silver nitrate and sodium chloride, thus:- Ag: NO, Na: Cl - Na: NO/AgCl; where there remains a solute NaNO, and a precipitate AgCl which of course is not ionized. The AgCl does not carry the cymbol of ionization, and therefore is recognised as a solid here in a solute. Out notation therefore says that if solutions of silver nitrate and sodium chloride be mixed at the ordinary temperature (the symbol says such), dissolved sodium nitrate will result along with a precipitate of silver chloride. We will now introduce an abbreviated means of indicating colour. This may be done by writing the initial and final letters. of the colour. Where it is possible that ambiguity might be possible, the colour may be indicated by three letters. Thus the colours of the spectrum would be put as rd, oe, yw, gn, be, io, vt. Even qualifying adjectives may be similarly abbreviated without confusion, as pe be would be pale blue, or rd orange red, oe gn olive green, gn bn green brown, bn bk brown black, yw we yellowish white, by yw brassy yellow or bs yw, gd yw golden yellow, etc. This method will be appreciated from our examples given hereunder. Instead of the sign of equality used in writing chemical equations we use the symbol or placing after the latter the conditions which start or bring about the reaction. Heat is expressed by /t, abstraction of heat or cooling by /-t, warming by /wt, white heat by /it, meaning incandescent heat, red heat by /rt, bright red heat, /brt, the electric furnace heat /et, boiling /bp, melting or fusing /mp, electric spark /st, silent discharge /dt, sunlight /sl, etc. Where we wish to indicate the temperature necessary to bring about a reaction we state the same after the line, thus, /85d, this meaning that at 85 degrees Centigrade the action starts. In A number in front of the line refers to the number of big calories produced by the reaction. If this be nothing and indicated thus, 0/18d, it is the same as saying that at 18 degrees Centigrade no action takes place. Should it be necessary to heat up to 1,000 degrees to start the reaction, and then, say, 150 big cals. are evolved, we state these facts thus:-150/1000d. short, wherever there is a big number followed by the line, that number refers to big cals. If heat is absorbed we indicate it as a minus quantity. Thus -120/bp means that 120 big cals. must be supplied to the reaction which will not start below boiling point. If we wish simply to refer to heat either evolved or absorbed without stating the exact amount we do so respectively, thus: n/- or -n/-, the reactions here taking place without the application of heat. We can of course make no reference to this thermal part of the equation, as is oftener than not the case. A few examples will illustrate the value of our notation as a space saver. -- The last refers simply to the decomposition by heat of H.MnCl.. iii MnO2/4HCl -t MnCl ̧/2HOH iv 3Fe/4HOH /bp Fe,O,/4H The bp might here mean that the water is boiling, a dotted line under the water will indicate the fact that we are dealing with steam. V Mn Cl/Ca(OH)2 solutions of Mn(OH). manganese Means that chloride and calcium hydroxide mixed at the ordinary temperature of the air give a precipitate of manganese hydroxide and calcium chloride passes into solution. When steam is passed through a mixture of manganese and calcium hydroxides to which air has easy access, CaMnO, is formed. This may be expressed : vi 2Mn(OH)2/2Ca(OH)2 / xHOH / Air 250d 2CaMnO,/4HOH/ XHOH without any reference to the state of the reacting substances. The temperature indicates the fact that the water is in the form of steam. viii 2CaMnO3/2CaO/2MnCl,/O /t These reactions proceed in the usual reading direction, namely, from left to right. If there were a possibility of the reaction taking place in the opposite direction, that is from right to left, we must express such fact by regarding the line as a circular chain, and supply another link which must be understood to precede the first half of the expression. When barium oxide is heated in air or oxygen, it forms the dioxide which on further heating decomposes to the monoxide. This may be expressed thus: BaO/O /t BaO, /t If we wish to state the temperatures at which these reactions take place we can do so thus: BaO|0 |700d BaO, |1000d In actual practice these temperatures are under not necessary, as the oxygen is pressure, which is relieved for reduction. When steam is passed over heated iron hydrogen is given off, but hydrogen will reduce red hot iron oxide, therefore the action is reversible. Such can be 60 expressed : 3Fe/4HOH /td Fe,O,/8H /td td signifying that the two temperatures are the same. MgCl2/HOH /t MgO/2HCl / -t is simple meaning that the reaction is reversible only when temperature is lowered. The oldest reversible reaction is Dr. Priestley's for the preparation of oxygen. Mercury heated becomes red through formation of oxide. If 200 grams of mercury be taken sufficient heat is developed to raise 30 kilograms of water through one degree Centigrade, that is to develop 30 cals. written in our notation 30/. If we further heat the oxide we get back the mercury and at the same time supply 30 cals, or develop -30 cals. Thus the proposition may be given. xxiii Hg/O 30/t HgO -30/t in reality understanding this to take the place of two sequences thus :— (a) Hg/O 30/t Hgo and in xxiii we read the -30/t as being before the first Hg/O. Thus the expression for a reversible reaction is supposed to be a circular chain, the last symbol preceding the first. We will continue with a few reversible reactions. xxiv Ba/O 124/- BaO|O 17/t BaO,|Air -17/t Bả0/0 Here barium burns, producing 124 cals, barium oxide heated gives BaŎ, and 17 cals, and the peroxide must be further heated and supplied with 17 cals to reproduce the oxide. xxv .Mg/2HOH /bp Mg(OH)2/2H /it Here we mean to state that at a white heat hydrogen will reduce the hydrate (but not completely). In the ordinary course of events the hydrogen from the first part of the reaction gets away, and is powerless to reverse the action, but if not allowed to escape it will certainly reverse it. When such a reaction takes place in a confined space it may be incomplete and reversible. We can express these two facts by brackets and the percentage sign,thus :-((.Zn/2HOH % bp /2H)) xxvi Zn(OH)2 We can state the atmosphere of that confined space between the first pair of brackets, thus: xxvii (N( .2A1/3HOH %rt Al2O/ 6H)) XXX (HOH( 3Fe/4HOH /rt Fe ̧01/ 8H)HOH) In the last example, which is that of a reversible reaction, no reversion takes place. The placing of the atmosphere HOH at both ends signifies that this atmosphere constantly passes over the reacting substances, as through a hot tube. As the rt indicates red heat, we need not show that the HOH is steam, and as we may see that we are dealing with a flowing atmosphere, we infer that the hydrogen is carried forward away from the possibility of any reversal of the reaction. In such as the following xxxi 2C1/HOH /18d HOC/HCl /30d which means that at the ordinary temperature, 18 degrees Centigrade, chlorine forms with water hydrochloric and hypochlorous acids, these re-forming chlorine and water at 30 degrees, the reaction is not really reversible. As we alter the conditions we alter the state of the reacting substances. Xxxii HOC /1 HC/O (light breaks up) and whatever order we give them the ions are capable of touching and moving round one another, ready to form fresh alliances other than those which existed before the salts were mixed. It should be noted that if the sodium takes on the hydroxyl group OH to form an alkali there is free hydrogen from the water ready to form a balancing acid, either sulphuric or hydrochloric. Had there been sufficient water present reaction xxxiii would not have taken place, and the ions would have maintained their aloofness, the sodium leaving the chlorine free. The maximum ionization with very dilute solution may be shown by double sign, thus: Na HSO,/H:: Cl/xH:: XOH : and there the reaction would end, and not with the precipitation of the sodium chloride. We give a few more reactions connected with the halogens. xxxiv K2Cr20,/14H: 14Cl /50d 2Cr Cl2/2K: 2C1/7H: 7OH/6C1 XXXV CrCl/H2SO, O/bp xxxvi CrCl/HNO, O/bp Xxxvii CrCl,/H /t CrCl2/HCI xxxviii CrCl,/3H /it 3HCl/Cr xxxix NiO/2HCl/2NH, /t NiCl2/ HOH/2NH, This might have been written thus:(NH,( NiO/2HCl /t NiCl2/HOH )NH1) indicating the fact that the reaction takes place in a current of ammonia, but such would suggest that the ammonia was there only to prevent the action of the air, whereas the ammonia affects the result as a catalyst, and is therefore included on both sides of the sequence. xl NiCl/0 /t NiO/Cl xli NiO/2HCl/xHOH /18d NiCl/ yHOH xliii NiCl2/HOH /t NiO/2HCl |