153 STATE BOAED OF AGRICULTURE. 



to give the requisite motion to the knives. As tlie knives move no faster than 

 is uecessar)', tliis may not at first look reasonable ; but I think when you con- 

 sider how much of a load must be pulled, and how many pieces of machinery 

 must be made to move before the knives stir, you will admit that there must be 

 a great deal of lost work, for the only work that is effective is that which gives 

 motion to the knives, and this Ave term the useful work. 



There is more or less work lost in every machine. In the steam engine, 90 

 to 97 per cent is lost ; in ordinary machines 40 to 90 per cent is lost, depending 

 to a great extent on the character and construction of the machine, while in the 

 turbine water-wheel, the most perfect of known machines, but 13 per cent is 

 lost. 



This lost work, that is, the work that goes into a machine but does not come 

 out, is mostly used up in overcoming friction. The rubbing of wheel on wheel, 

 the turning of axle in its box, or the slipping of band, all indicate a waste of 

 power for which there is no complete remedy. The waste of power in friction 

 may be greatly lessened, however, by a careful choice of materials, by skillful 

 manufacture, and by the use of unguents. On the other hand, friction may be 

 greatly increased by any unnecessary complexity (for example, in a mowing 

 machine, by the addition of a couple of extra cog wheels above the necessarj'" 

 number), by bungling construction (as when the cog wheels do not fit nicely, 

 or the axles are loose in their boxes), and by neglecting to apply unguents. 



Unguents should be used wherever there is any sliding friction. This, of 

 course, covers all cases where one body slides on another, and where one axle or 

 other rod rolls in a box or in any stationary piece ; but it docs not cover the 

 case of wheels that come in contact at their circumferences, or of the teeth in 

 cog wheels, as in both these cases there is no sliding friction. 



Unguents should be thick for heavy pressvires, that they may resist being 

 forced out, and thin for light pressures, that their viscidity may not add to the 

 resistance. 



Unguents may be divided into the four following classes : 



I. Water, which acts as an unguent on surfaces of Avood and leather. It is 

 not, however, an unguent for a pair of metallic surfaces, for Avhen applied to 

 them it increases their friction. 



II. Oily unguents, consisting of animal and vegetable fixed oils, as tallow, 

 lard, lard oil, seal oil, whale oil, olive oil, and castor oil. The vegetable drying 

 oils, such as linseed oil, are unfit for unguents, as they absorb oxygen and 

 become hard. The animal oils, on the Avhole, are better than the vegetable oils. 



III. Soapy unguents, composed of oil, alkali-, and water. For a temporary 

 purpose, such as lubricating the ways for the launch of a ship, soft soap made 

 irom whale oil and potash, with or Avithout talloAV, is the best of unguents ; 

 but for a permanent pur2)ose, as for lubricating the axles, of raihvay carriages, 

 it should contain more oil or fatty matter than soft soap does. The best grease 

 for such purposes does not contain over 30 per cent of Avater. 



IV. Bituminous or Pitchy unguents, which are noAv used so rarely that it is 

 ■unnecessary to describe them, though the old tar bucket once had a conspicuous 

 place under the axles of our Avagons. 



Unguents on Teeth of Wheels. 



It is quite a common practice among threshers, and Avith some farmers, to 

 apply talloAV or other animal grease to the teeth of Aylieels. In any place Avhere 

 sand or other grit is apt to accumulate, as on a mowing machine or a reaper. 



