Ill 



i un 



LATENT IIKAT. 



rtitote far the more espe-ive oak in sMpboMtafc; oWefly in 

 Teasels. As alsipr for railways, axles far mill-work, hop poles, and 

 Uke* tor phnto IB rneral, larch |i.ssiinii great value. Especially 

 fer rattway faiBirs is this usefulness oheerrahle; because, as the 

 | M |iin an nstosd on ground (abject to frequent alternations of wet and 

 dryTthe power of the timber to resist thi. action becomes a matter of 

 rest Importance. Larch is not so useful in common house-carpentry 

 M deal bwsiue it U a wood difficult to saw and plane ; a less durable 

 wood k (elected on account of its east in working. The use of larch 

 ha* ben much (OMNin*]*d by the grand operations of the dukes of 

 Athol About a hundred and thirty yean ago, the hills in the 

 1 >unkeld and BUir-AUiol district* were barren and almost valueless, 

 scarcely worth a shilling an acre for any industrial purposes. James, 

 the duke of Athol of those daya, planted a few larches for ornamental 

 nmposes. and then planted two thousand more for timber. It was a 

 thought worthy of a great landed proprietor ; for it could only be in 

 the time of his sucoeseon that the trees would be old enough to cut 

 down far timber. Much difficulty had to be encountered ; for tin 

 fane, broom, juniper, and heath, greatly retarded the growth of the 

 young larches; but this obstacle was conquered by perseverance. 

 The next duke planted eleven thousand larches between 1764 anil 

 1774 ; while the eon of thi* latter, in the fifty-two yean from 1774 to 

 18M, planted the enormous number ot fourteen milliont, some of them 

 ven on the summits of mountains. It was calculated about the last 

 rt*"""* date, that during the second half of the present century all 

 Uissu will successively beoome magnificent timber trees, suitable for 

 ship-building nd large engineering operations ; and that, if all went 

 well, the planting would virtually be a creation of property to the 

 mount of six or seven millions sterling. 



On the continent, larch U applied to a great variety of purposes. 

 The Rhenish wine-casks are made of this wood, and are said to be 

 more durable than any other. In some parts of France and Switzer- 

 land honees are built of larch, by placing bulky squared trunks one 

 upon another ; the heat of the sun, melting the resin in the wood, 

 causes it to run down the sides and to fill the interstices between the 

 logs, thereby keeping out both air and moisture. Larch is in general use 

 for water pipes in those countries. The larch vine-props are left in 

 the ground for yean together; all around them arc props which 

 perish year after year, while the larch itself remains sound. 



Other part* of the tree are also applied to useful purposes. The 

 bark is used in France and England for tanning. The leaves are eaten 

 by cattle and sheep. The burnt wood yields very heavy charcoal, 

 excellent for iron foundries. Venice turpentine, so called, is obtained 

 from the larch. In certain parts of France, during four months of 

 summer, the obtaining of this turpentine is a regular employment ; a 

 full-grown tree yielding in this time six or eight pounds. Incisions 

 about an inch in diameter are made in the trunk of the trees ; small 

 trough* or descending channels are placed in connection with these 

 incisions; vessels are placed underneath ; and after regular intervals of 

 a few noun, the vessel* beoome filled with clear turpentine. 



It may here be mentioned that within the last few years some little- 

 understood disease has affected the larch plantations in many parts of 

 TiWtil ; sod that a volume has just been published on this special 

 subject by Mr. Macintosh, the author of various works on gardening 

 and planting. 



LAUD. [FAT; TJorKiTS.]| 



LAKES, among the Romans, were household gods; the guardians 

 of their hearths and families. There is much dispute upon the etymo- 

 logy of this term. Apuleius derive* it from far, familiarit. Ovid 

 peeks of the Lares as the offspring of Mercury and Lara. From a 

 passage in Virgil'. \., 255. it would seem that these Lares of 



the Romans were the mann, or souls of their deceased ancestor* : it is 

 certain that their worship was closely connected. According to Ovid 

 (' Fasti/ v., 1 46) there were generally two of them, who were some- 

 times represented with a dog at their feet Others were clothed in the 

 kin of a dog. They wen of small sire, and generally represented in 

 short habits a* ready to minister to the needs of the household, and 

 usually held a cornucopia in their hands as a symbol of good house- 

 keeping. The festival of the Lares was celebrated on the kalends of 

 Hay (Ibid., v., 129) when they were crowned with garlands and sacri- 

 fices were offered to them. In the inner part of large houses there 

 WM frequently a Lanrium or shrinn for the worship of the Lares. 

 Pitiecus records an inscription, ' LARIBVS FRO SALVTK KT ISTOI.VMI- 

 TATB DOMTS g. SRRToiiii.' There seem to have been two classes of 

 Leres. the Lara damrttici rt famitiara, which were the family Manes; 

 and the Lorn publiri, which included Lam urban!, rwraltt, rlalet, rom- 

 fitala, mutrimi, Ac. which presided in the localities indicated by their 

 titles. TMAim; PWATW.] 

 LARGK. In music, see Logo. 



I.AI'.'ilir.TTo (Italian), a musical term, a diminutive of Largo 

 [ I.m-.oJ, alow, but less so than Largo. 



I. \ !:". in mimic (IU1. adverb, largely, widely), is the second in 

 order of the fire nltssus into which musical movement in divided 

 -I, and dignifies ita^f. 



LAH 



LATKNT IIKAT Wl,-n a body Is exposed to the action of heat 

 o M to change ita state, as from a solid to a liquid, it rises to a certain 

 a* It* melting or fining point, and remains fixed 



at that temperature until the whole of the solid shall have been 

 liquefied. [LlQUKF ACTION.] During this operation a quantity of heat 

 mud evidently enter the body in order to produce liquefaction ; and 

 as it produces no effect on the thermometer, it is said to be combined, 

 and rendered latent, and is also known as the heal of liquefaction, or 

 that beat necessary to the liquid state, so that when the body again 

 becomes solid, the heat thus combined u given off in a sensible form. 



Latent heat is one of the capital discoveries of Dr. Black. There 

 are various mode* of estimating it* amount in different bodies, one of 

 which is by means of the calorimeter, an instrument which bean to 

 combined heat the same relation that the thermometer does to sensible 

 heat. The calorimeter was shortly described under HEAT, and will be 

 figured and described under SPECIFIC HEAT. In order to ascertain 

 how much heat is absorbed and rendered latent during the liquefaction 

 of ice, for example, all that is necessary is to place a pound of water of 

 any known tempenture in the calorimeter, which U filled with ice, 

 and observe how many degrees the hot water falls through in dissolving 

 a pound of ice. It will be found that the water must give off 142-65* 

 of sensible heat in order to convert ice at 32 into water at 82. Hence, 

 during the liquefaction of ice, as much heat is rendered latent as would 

 suffice to raise it* own weight of water from 82 to 32 + 142-65 = 

 174-65. 



Since then a pound of ice at 32 absorbs 142 J 65 in becoming a 

 pound of water at 32, it follows that the same quantity of heat is 

 given out or rendered sensible, when the ice again psssos into water. 

 There are various modes of proving this : Suppose a vessel of water at 

 60 be immersed in mercury at 60 below the freezing-point of water, 

 or 28; a thermometer in the mercury will rise, and one in the 

 water will fall until the latter indicates 32. We will call these two 

 thermometers No. 1 and No. 2. No. 2, then, or that in the water, will 

 remain stationary during the freezing ; but No. 1 will continue to rise 



water. When all the water has beoome solid, then, and not before, 

 will the thermometer No. 2 again begin to fall ; but the thermometer 

 No. 1 will rise uninterruptedly until both thermometers meet at some 

 I lint below 32. The cold of winter is considerably mitigated by : In- 

 sensible heat which is given out by freezing water, and when the tem- 

 perature rises with the return of milder weather a considerable portion 

 of the heat is employed in producing liquefaction. 



Similar phenomena accompany the liquefaction of other bodies. 

 When a mass of lead, for example, is put over the fire it rises to 620 ; 

 it' then begins to fuse, and it remains at that temperature until the 

 whole man has become liquid : the heat thus absorbed and rendered 

 latent is called the latent heat of fution. The following tablo gives the 

 latent heat of certain liquids : 



Fhr. 

 Water 141-65' 



Nitrate of soda 

 Nitrate of potash 

 Zinc . 

 Silrer . 

 Tin . 



Cadmium . 

 Bismuth 

 Sulphur . . 

 Load 



Phosphorus . 

 Mercury 



113-34 



85-96 



50-63 



37-93 



25-65 



24-44 



SI-7S 



16-89 



9-65 



n-05 



5-11 



1-000 

 0-794 

 0-598 

 0-355 

 0-265 

 0-179 

 0-171 

 0-159 

 0-118 

 0-067 

 0-063 

 0-035 



It will 1* seen from the above table, that the latent heat of ice is 

 very considerable, while that of lead is very small : hence ice melts 

 slowly, lead rapidly. Ice cannot melt until it has received as much 

 heat as would raise it* own weight of water 142-65 ; while lead melts 

 with as much heat as would raise its own weight of water 9*65. Did 

 ice melt with the same comparative facility as lead, the first thaw 

 would cause inundations by the sudden melting of the snow and ice of 

 winter. 



\\ li.-n a liquid passes into the state of vapour there is a further 

 absorption of heat, still more remarkable than in the case of lique- 

 faction. If heat be applied to water at 32, the temperature will rise 

 through 180 to the boiling-point, which under mean pressure is 212*. 

 MI or LIQUIDS.] At this point the water will pass off mjiidly 

 in til- form of steam, and during the \vli- <1< ,<\ tliin time tlu> thermometer 

 will remain fixed ; or, in other words, the steam will have precisely the 

 same temperature as the boiling water. We can easily calculate the 

 piaiiiiiy of boat thus absorbed and rendered 'latent by the steam, by 

 noting the time required to raise the water through the 180 between 

 32 and 212*, and also by ascertaining how long it took for the 1 

 water to |*s off into steam. Supposing these times were equal, the 

 same quantity of heat must evidently nave been employed in the one 

 case as in the other ; but what is the fact? It requires 6 4 times as 

 long to convert the water into steam as it did to raise it from 32* to 

 212* ; in other words, the latent heat of steam is 54 x 180 = 990. 



Thin enormous quantity of latent heat is again given out when steam 



i into water, and hence steam becomes a powerful source of 

 beat. Indeed any given weight of water in the form of steam at 



condensed, will raise 54 times its own weight of water from 

 82* to i.'1-j . 



The heat absorbed during the vaporisation is less in proportion as 



