SUFFIX. 



SUGAR. 



882 



as much an idea of geometry as any other. Let A and B be the two 

 ends of a lever (a rigid bar without weight), and c its middle point, 

 which is the pivot ; that is to say, the middle point cannot move, the 

 only possible motion of the lever being revolution, in the plane of the 

 pressures, about that middle point. On these hypotheses, we may 

 certainly say that the axiom is self-evident, for want of sufficient 

 reason, that is. of a possibility of sufficient reason for anything in con- 

 tradiction of it. We have, before the pressures are applied, no cause 

 of motion, by hypothesis : we are to conceive a lever, which, if it move 

 at all, does so by reason of the pressures. AVe have made these 

 pressures equal, and applied them symmetrically : there is then, and 

 can be, no reason why one should predominate, which does not hold as 

 much of the other. In the very notion of equality of pressures there 

 is interchangeability ; that is, each may be substituted for the other 

 without alteration of effect. Suppose then the left-hand pressure to 

 predominate : it will do so if the pressures be interchanged. But 

 after the interchange the same reasons which made the left hand pre- 

 dominate, will make the right hand predominate : or both ends will 

 move in the direction of the pressures, which is impossible. 



We believe the preceding to be as legitimate a use as can be made 

 of the sufficient-reason principle ; but before statics can be established 

 on axioms, there is another of them required, which we have never 

 been able to satisfy ourselves comes " from within." It must be 

 assumed that the pressure on the pivot is equal to the sum of the 

 pressures on the ends, whatever the length of the arms may be : this 

 we believe ve learn from existing matter in quite a different sense from 

 that in which we speak when we say that we learn the conception of 

 pressure or of a straight line from our communication with the exter- 

 nal world by our senses : to us it more resembles the assertion that 

 the sea is salt, or that a horse has four legs. It certainly does not 

 arise from the sufficient- reason principle ; for there is a reason why 

 difference of pressures on the pivots may arise in levers which only 

 differ in the arms, namely, that very difference of the anus. In fact, 

 there is a presumption against the truth of the proposition <i />riri, 

 derived from a principle tae frequent and usual truth of which may as 

 well be called knowledge " from within," as the conception of pressure 

 or of a straight line : this principle is, " differences generally make 

 differences, but 'not necessarily." The beginner in geometry has this 

 in his mind when he feels that he has learnt something in finding nut 

 that the sum of the angles of a triangle is always the same, whatever 

 the triangle may be : he would have expected it to be otherwise. 

 Triangles of different sides have generally different areas, different per- 

 pendiculars, different inscribed and circumscribed circles, and different 

 angles : why not different sums of angles ? In truth it is a constant 

 and latent assumption throughout the exact sciences that " differences 

 are to be supposed to moke differences, except where the contrary is 

 proved." And the assumption that the pressure on the pivot of a 

 lever is independent of the arms, ia either in defiance of this general 

 principle, or a result of experience. 



Thinking, then, that the sciences of pure mechanics can be founded 

 up. .11 few and incontrovertible postulates, in such a manner as to entitle 

 tin-in to the name of pure sciences, or some other which shall mark the 

 real distinction between them and the other sciences of matter, we 

 cannot yet be of opinion that their postulates are all derived from their 

 own evidence, or obtainable from the sufficient-reason principle. There 

 are, however, many points connected with this part of them which are 

 difficult of exposition for want of acknowledged terms. 



SI'!-' FIX, a term lately employed in mathematical language to de- 

 ii"t- the indices which are written under letters, as in a,, a, a, a,, &c. 

 Though these signs have been so long used, we never saw a distinctive 

 name given to them before the publication of Professor Halls 

 ' Differential Calculus.' 



SI KKItACAX. [BISHOP.] 



SUGAR. Referring to SUGAR in the NATURAL HISTORY Division 

 of this Cyclopaedia for an account of its distribution in the organic 

 kingdom, and to a separate article [SUOAR CULTURE AND M.\ 

 TUBE] for information concerning the extraction from the sugar-cane, 

 in I purification of common or cane-sugar, we shall at present only con- 

 sider sugar from a chemical point of view. 



Sugar in Persian, thiikkur, and originaJy sarkara (Sanscrit) may be 

 defined as a body having a sweet taste, and which, under the influence, 

 direct or indirect, of ferments, splits up into alcohol and carbonic acid. 

 As few plants are wholly destitute of sugar, and as many contain it in 

 considerable proportions, it is not surprising that many so-called 

 varieties of sugar should have been described from time to time. Thus 

 we read of sugar of starch, sugar of raisins, sugar of milk, sugar of 

 gelatine, cane-sugar, grape-sugar, manna-sugar, &c. &c. Many of these, 

 however, have been shown to be identical, and at present nearly all 

 may be included under four varieties, namely : tiucrote, or cane-sugar, 

 including sugar from the beet-root, turnip, carrot, maple, birch, palm, 

 Indian corn, and many fruits of tropical plants ; Glucose, including grape- 

 sugar, itarch-sugar, and the sugar generally found in dried fruits; 

 Pruetote, the state in which sugar exists in recently plucked fruits ; and 

 Lactott, the sweet principle found in the milk of animals. 



Berthelot divides the whole clan of sugars, properly so called, into 

 two fundamental groups, of which sucrose and glucose are the respec- 

 tive types. The glucone group is characterised by fermenting directly 

 in contact with yeast ; by I .ciny destroyed by strong alkalies, even in 



ARTS AJfD SCI. DIV. VOL. VII. 



the cold, and readily at 212 Fahr. ; by the reducing action on potas- 

 sio-tartrate of copper ; and by the circumstance that when dried in a 

 water-bath the members of this group are isomeric, having the formula 

 Cj.JIj.-O^. The members of the glucose group differ from each other 

 in their crystalline form ; in their rotatory power on polarised light 

 [SACCHARIMETRY] ; in the modifications they undergo when exposed 

 to the influence of heat or acids ; in the nature of their combinations 

 with water, bases, and chloride of sodium ; and in the manner of 

 their conversion into mucic acid, &c. Under the sucrose group, 

 Berthelot includes all sweet principles analogous to cane-sugar ; they 

 with difficulty ferment under the influence of yeast ; are scarcely 

 changed by alkalies, or by potassio-tartrate of copper, even at a tem- 

 perature of 212 Fahr. ; are, by the action of acids, readily converted 

 into new sugars belonging to the glucose group ; and are isomeric only 

 when heated to 266 Fahr., having then the composition C^H^O,,. 

 The members of the sucrose group are distinguished from each other 

 by their crystalline form ; rotatory power ; unequal resistance to heat, 

 acids, and ferments; in their behaviour to bodies with which they 

 combine; and in the formation of mucic acid, &c. Sugar of milk 

 (lactose), however, stands in a position intermediate between the above 

 groups; resembling the glucose series in the action of alkalies and 

 copper-salts upon it, it is nevertheless analogous to sucrose in resisting 

 the action of heat and ferments, and capability of being converted into 

 a fermentible sugar. 



The four chief varieties of sugar differ slightly from each other in 

 composition, and very widely in appearance and sweetening power. 

 Sucrose has the formula C^H^O^cr possibly double that (C^H^O.,,,) ; 

 its appearance and taste are well known. Glucose, or grape-sugar 

 (C J ,H ls O 1 ,+ 2Aq.) has considerably less than half the sweetening 

 power of cane-sugar, and is generally met with as a somewhat soft 

 and granular, rather than crystalline mass. Fructose (chularicosc) 

 (CuH^.O,^ is also less sweet than sucrose, and is, moreover, uucrystal- 

 lisable. And finally, lactose (C.. 4 H 24 O 2) ) occurs in hard, gritty, mam- 

 millated crystalline masses, and is considerably inferior in sweetness 

 to any of the other sugars. 



Cane Smjar (C 12 H n O u ) is colourless, inodorous, of a purely sweet 

 taste, moderately hard, and brittle. The crystals, when rapidly formed, 

 as in common refined sugar, are small ; but when obtained by the 

 slow evaporation of a strong solution, they are of considerable size 

 (sugar candy). The specific gravity of sugar is about 1'6 : it under- 

 goes no change by exposure to the air ; and, when moderately heated, 

 loses only a little hygroiuetric moisture : it is soluble in one-third of 

 its weight of cold water, and in all proportions in hot water : a solution 

 saturated at 230 forms, on cooling, a mass of small crystals. It is 

 soluble in alcohol, but much less so than in water ; absolute alcohol 

 takes up only l-80th of its weight, even when boiling, and this sepa- 

 rates in small crystals as the solution cools : spirit of wine, of specific 

 gravity 0'830, dissolves nearly one-fourth of its weight. Sugar i.s 

 phosphorescent when two pieces are rubbed together in the dark. 

 Heated to about 320 Fahr., sugar melts into a viscid colourless liquid, 

 which, cooled suddenly, becomes a transparent mass (barley-sugar) ; by 

 keeping, it becomes opaque. At 400 to 420 sugar is converted into 

 CAKAUEL, or burnt ttujar (C^H^O,), two equivalents of water being set 

 free. When exposed to a higher temperature, sugar undergoes decom- 

 position, yielding various gaseous products, and leaving a large pro- 

 portion of charcoal. Acids produce very different effects upon sugar : 

 thus nitric acid decomposes and is decomposed by it, the principal 

 products being nitric oxide, carbonic, oxalic, and saccharic acids : 

 sulphuric acid, when concentrated, attacks sugar itself, or even a strong 

 solution of it, sulphurous and carbonic acid gases being formed and 

 evolved, and a large quantity of carbou set free ; l-100th of a grain 

 of sugar, on account of the large proportion of carbon which it 

 contains, is capable of imparting colour to an ounce of sulphuric acid. 

 When sugar, dissolved in dilute sulphuric acid, is kept for a long time 

 at a high temperature, it absorbs oxygen from the air, formic acid is 

 produced, and there is deposited a brown insoluble matter termed 

 ulmin. Ulinin is sometimes formed when recently expressed cane 

 juice is heated, a small portion of lime, however, neutralises the acid 

 in the juice, and prevents its formation. Hydrochloric acid dissolves 

 sugar, and forms with it a thick black resinous paste. A simple 

 solution of sugar hi water undergoes change slowly when exposed to 

 the air, but on the addition of yeast it undergoes rapid fermentation, 

 and is converted, first into grape-sugar, and then into alcohol. 



Sugar in many cases combines with the alkalies, earths, and metallic 

 oxides, and, in some cases, forms definite compounds with them 

 called saccliaratet, or laccharidei. With ammonia, according to Ber- 

 zelius, sugar combines to form a compound of one equivalent of each ; 

 but by exposure to the air the ammonia escapes, and leaves the sugar 

 unaltered : potash and soda appear also to combine with sugar, and 

 they destroy its sweetness ; this is restored when the alkalies are satu- 

 rated with an acid : but if they be left long in contact, the sugar 

 becomes changed into a substance resembling gum. 



Lime, baryta, and oxide of lead dissolve in considerable quantity in 

 a solution of sugar : wheu the first-mentioned of these bodies, in the 

 state of hydrate, is digested at a moderate heat in a solution of sugar, 

 a bitter alkaline solution is obtained, in which the sugar is combined 

 with an equivalent of lime (CaO, C^H,,*},,). Professor Daniell obtained, 

 by the action of these bodies, gum and crystals of carbonate of lime. 



3 L 



