Dec. 9, IbSl.J 



KNOWLEDGE 



lOlt 



In tliis case we seem to recognise on both sides reasoning 

 which approaches at times tlie absti^act. In the calculation 

 of means to an end, and change of plan in consequence of 

 unexpected obstacles, there is practical reasoning. As 

 ^Vigan well says, " Had the human race spun webs, and 

 dared one another to single combat, they could not well 

 have shown more judgment and skill in the attack and 

 di-fence. The .strengthening of the lines to bear the 

 shaking, and doubling the smaller spider's lines while using 

 tlirm as lines of advance, belonged also to the order of 

 ]iractical reasoning, though of a rather advanced kind. 

 But there was abstract reasoning, it seems to us, or a near 

 approach to it, in the conduct of the smaller spider, first of 

 all, in considering, as it were, how far he might trespass 

 en the patience of an enemy whom he recognised as his 

 superior, and again in the conduct of the larger in deciding 

 when the time had come to giv(> his small enemy a 

 lesson, and in retreating finally without persisting, as if 

 1 eflecting that his purpose was as well achieved as though 

 he had actually driven the smaller spider from his web. 

 His removing the lines which had supported the smaller 

 web, though he had previously allowed them to remain, 

 looks very much like a result of abstract reasoning. 



We find illustrated by such instances the remark of 

 1 )r. Prichard, that among insects, if we take the different 

 trilies collectively, manifestations of all the psychical 

 ([ualities which we observe in mammifers and birds (re- 

 garding as a whole the properties di\-ided among dif- 

 ferent departments), may be recognised in the most strict 

 analogy. Attention, memory, the faculty of combining 

 means to attain ends, cunning, the desire of revenge, care 

 of offspring, and all the other psychical qualities which 

 have been traced in the former class of animals (niammi- 

 firs) are likewise to be observed in the latter as typical or 

 ihai-acteristic phenomena — sometimes m one combination, 

 sometimes in another ; or, in different groups, sometimes 

 strongly, sometimes more feebly expressed. 



SOLIDS, LIQUIDS, AND GASES. 



By W. Mattieu Willi.\ms. 



VS alreadv explained, all gases are now proved to be 

 analogous to steam ; they are matter exj)anded and 

 iindcred self-repulsive by heat. All eb'ineiitartj matter 

 liiay exist in either the three forms — solid, liquid, or gas, 

 aicording to the amount of heat and pressure to which it is 

 subjected. I limit this wide generalisation to elementari/ 

 substances for the following reasons. 



Many compounds are made up of elements so feebly held 

 together that they become " dissociated" when heated to a 

 temperature below their boiling-point. Or their condition 

 may be otherwise defined by stating that the bonds of 

 chemical energy, which hold their elements together, are 

 weaker than the cohesion which binds and holds them in the 

 condition of solid or liquid, and are more easily broken by 

 the expansive energy of heat To illustrate this, let us 

 take two common and well-known oils, olive oil and tur- 

 pentine. The first belongs to the class of "fixed oils," the 

 second to the " volatile oils." If we apply heat to liquid 

 turpentine, it boils, passes into the state of gaseous turpen- 

 tine, which is easily condensible by cooling it. If the liquid 

 result of this condensation is examined, we find it to be 

 turpentine as before. Not so with the olive oil. Just as 

 this reaches its boiling point, the heat, which would other- 

 wise convert it into olive-oil vapour, begins to dissociate its 

 constituents, and if the temperature be raised a little 



higher, we obtain some gases, but these are the products of 

 decomposition, not gaseous olive oil. This is called " de- 

 structive" distillation. 



In oli\e oil, the boiling-point and dissociation point are 

 near to each other. In the case of glycerine, thf se points 

 so nearly approximate that, although we cannot distil it un- 

 broken under ordinary atmospheric pressure, we may do so 

 if some of this pressure is removed. Under such diminished 

 pressure, the boiling-point is brought down below the disso- 

 ciation point, and condensible glycerine gas comes over 

 without decomposition. 



Sugar affords a very interesting example of dissociation, 

 commencing far below the boiling point, and going on 

 gradually and visibly, with increasing rapidity as the tem- 

 perature is raised. Put some white sugar into a spoon, and 

 heat the spoon gradually over a smokeless gas-flame or 

 spirifi-lamp. At first the sugar melts, then becomes yellow 

 (barley sugar) ; this colour deepens to orange, then red, 

 then chestnut-brown, then dark; brown, then nearly black 

 (caramel), then quite black, and finally it becomes a mere 

 cinder. Sugar is composed of carlion and water ; the heat 

 dissociates this compound, separates the water, which passes 

 off as vapour, and leaves the carbon behind. The gradual 

 deepening of the colour indicates the gradual carbonisation, 

 which is completed when only the dry insoluble cinder re- 

 mains. An appearance of boiling is seen, but this is the 

 boiling of the dissociated water, not of the sugar. 



The dissociation temperature of water is far above its 

 boiling-point. It is .5,072° Fah., under conditions corre- 

 sponding to those which make its boiling-point 212°. If 

 we examine the variations of the boiling-point of water, as 

 the atmospheric pressure on its surface varies, some curious 

 results follow. To do this the reader must endure some 

 figures. They are extremely simple, and perfectly intelligible, 

 but demand just a little attention. Below are three columns 

 of figures. The first represents atmospheres of pressure — 

 i.e., taking our atmospheric pressure when it supports 

 30 inches of mercury in the barometer tube as a unit, 

 that pressure is doubled, trebled, ttc, up to twenty times 

 in the first column. The second column states the tem- 

 perature at which water boils when under the different 

 pressures thus indicated. Tlie third column, which is the- 

 subject for special study just now, shows how much we 

 must raise the temperature of the water in order to make 

 it boil as we go on adding atmospheres of pressure, or the 

 increase of temperature due to each increase of one atmo- 

 sphere of pressure. The figures are founded on the ex- 

 periments of Regnault. 



It may be seen from the above that, with the exception 

 of one irregularity, there is a continual diminution of the 



