518 STATE BOARD OF AGRICULTURE. 



aiitlior lliids tlial better results were obtained by removing the rubber 

 tubini;' in either ease, otherwise the How will be hindered by shutting 

 onl llie tree mcccss of air. Tranlte reconinuMids the use of two mirrors 

 so arranged Ihat one can notice wlien the lirst drop falls while taking 

 the reading on the upper ])art of the scale. The author finds it easier 

 to allow the lirst drop to fall into the hand while taking the reading. 

 This is oidy necessary for surface tension work. The nundier of drops 

 is counted and the reading is also taken for the last drop. From the 

 data thus obtained, the size of the drop is deterjuined. The size of the 

 drop of distilled water is also determined and the two compared, the 

 size of the drops is obtained by dividing the number of the divisions of 

 the pipette delivered by the corresponding number of drops. The time 

 it takes for the solutions to pass through fifty divisions of the i)ipette 

 divided by the time for distilled water to pass through the same number 

 of divisions gives the viscosity. 



Size of drop of solution X Sp. Gr. 



Size of drop of dist. water X Sp. Gr. 

 Sp. Gr. of solution X t 



= Surface Tension of Solution. 



Sp. Gr. of Dist. Water X t' 



= Viscosity of Solution. 



As temperature influences the flow and amount of liquid used, the 

 tube is surrounded by a water jacket with a thermometer. 



Another important factor in the study of the soil solution is its 

 concentration because of the effect it has upon the development of 

 the living cell. This concentration concerns the force or pressure that 

 the solutes exert when placed under varying conditions. In connection 

 with the cell, either of the higher or lower plant life with which the soil 

 solution comes in contact the solutes exert a force against the plasma 

 membrane, called osmotic pressure. Here we have three factors to take 

 into consideration — solution, plasma membrane and the solvent. When 

 we have only the solution itself, a single factor, the force that it may 

 exert is called osmotic concentration, usually recorded in pres.sure of at- 

 mospheres. Both the osmotic pressure and osmotic concentration can 

 be determined by the freezing point method. 



Before discussing this method of determination, a few Avords may be 

 said in regard to the effect of solutions upon the living cells. When this 

 solvent, water in the soil solution, passes through the membrane, it 

 causes the liquid to rise or push out the walls of an elastic membrane. 

 In the case of plants, or microorganisms, they become rigid or turgid 

 with this pushing out of their cell Avails due to the hydrostatic pressure 

 of the solvent. In order for the cells to take up water, the concentration 

 of the cell sap or cell contents must be greater than that of the soil so- 

 lution. If the reverse were true, the moisture of the cell would diffuse 

 out. riasmolysis and ultimately death of the cell would result. In 

 case of plants, this is evidenced by their wilting and finally by their dry- 

 ing. The plants lose their turgidity. The plant nutrients that are in 

 solution diffuse through the cell wall and plasma membrane of the roots 

 as rapidly as the plant utilizes those already in the cell sap. This 

 process is slow^er than the diffusion of the water. If this water were not 

 replaced either by rain or from some other source, the soil solution would 

 become more concentrated and thus the process would be reversed, — 

 the water going out instead of going in. 



Note — t and t', = Number of seconds for a given amount of liquid to flow out of apparatus. 



