ON RESTORING PLANTS. 5 



stances of different temperature, come in contact with each other, the 

 temperature of the one is raised, and that of the other is lowered, un- 

 til the two substances become equal, and if they are of equal density, 

 the temperature will be a mean one — this is provided that neither 

 of these substances undergo a change from solid to fluid, or from 

 fluid to gaseous. In this case, a great quantity of perceptible heat 

 will be consumed, and converted into latent heat; and if the change 

 is from gaseous to fluid, or from fluid to solid, perceptible beat will 

 be produced from the giving off of the latent. Thus, if equal weights 

 of ice at 32, and water at 172, he mixed together, the whole of the. 

 ice will be melted, but the temperature of the mixture will be 32, so 

 that 140 degrees are lost, or converted into latent heat. 



If a tender plant that will not bear the frost, a Pelargonium for 

 instance, be exposed to an atmosphere of 32, or exactly the freezing 

 point, it will not be injured, but if the temperature sink below that 

 point, say 28, under ordinary circumstances, when the least circula- 

 tion of air is, the juices of the plant will be frozen, and it will be in- 

 jured by the application of perceptible heat, in its rising from 28 to 

 32 ; but if the temperature when at 28 is raised by the freezing of 

 water, when the act of freezing, by giving off latent heat, raises the 

 temperature to the freezing point, the plant is uninjured. It follows, 

 therefore, that the application of water should commence before there 

 is any alteration in the temperature of the surrounding atmosphere, 

 that is, in a morning before the sun rises, or before a fire is put on, 

 and continued until the temperature is raised to the freezing point ; 

 but if the temperature of a greenhouse should be sunk to 28, and a 

 slight syringing of water applied, only sufficient to raise the tempera- 

 ture, by the congealation of its particles to 30, a great injury will 

 be sustained; if left to rise afterwards by perceptible heat to 32, as 

 the agitation which will have taken place amongst the plants, will 

 have more effectually frozen their juices. The water which is used, 

 should not be much, if any, above the freezing point, or as cold as 

 can be procured, so that the temperature of the plant should rise 

 from 28 to 32, not by the application of a warmer substance so much 

 as the converting of latent into perceptible heat. It is also of very 

 great consequence that the leaves or no part of the plant should be 

 moved when in a frozen state, as the cellular tissue, of which they 

 are in a great measure composed, being of a very delicate texture, each 

 cellule being filled with watery juice, which becomes frozen, the least 

 bending of that part of the plant would rupture the membrane, which 

 are only (and in man}- cases not quite) elastic enough to allow of 

 the expansion of the water by freezing; it is, therefore, obvious that 



