40 L)structio)is tn Fidd Parties. 



The electrolytic cells are made as nearly of the same dimensions 

 as possible, but if there is much variation in either volume or 

 shape this table must not be used without a correction for the cell. 



If greater accuracy is desired than can be expected by the use 

 of the above table, proceed in the following way: 



Collect 6 or 8 samples of water from different parts of the area; 

 determine the electrical resistance of each, and take an amount of 

 each proi^ortional to the resistance, mixing them in a clean vessel. 

 There should be at least 2 quarts, and preferably 1 gallon, of this 

 mixture. Evaporate slowly on a stove until the mixture is aliout 

 as strong as the strongest water likely to be encountered. If there 

 is any possibility of encountering water as strong as a 1 per cent 

 solution — that is, 1,000 j^arts of salts in 100,000 parts of water — the 

 mixture should be evaporated until it gives a resistance in the cell 

 of about 23 ohms. The amount of this evaporation can be deter- 

 mined by the original resistance of the mixture. If the resistance 

 of the mixture is-100 ohms, it should be evaporated to one-fourth 

 its volume to make approximately a 1 per cent solution. If the 

 resistance is 400 ohms, the solution should be evaporated to one 

 twenty-third of its original volume. Water having a resistance 

 of 400 ohms would have a salt content, according to the above 

 table, of about 44 in 100,000, and would be considered an excellent 

 water for irrigation purposes. It would require 3 gallons of such 

 water, evaporated to 1 pint, to make a 1 per cent solution. 



To determine the actual per cent of salt in this solution, after 

 finding the resistance in a cell, evaporate in a weighed vessel — such 

 as a tin cup or a tin can — a separate, weighed amoimt of the water. 

 Weigh the vessel again after the evaporation, and this will give 

 the amount of residue in a known weight of water. The weighing 

 should be carefuly done on reliablfe druggists' scales. 



Take the concentrated solution and dilute with successive quan- 

 tities of distilled Avater, so as to change the concentration of the 

 solution and get the corresponding resistances in the cell. Use, for 

 example, 9 j)arts of the solution and 1 part distilled water, then 8 

 parts of the solution and 2 parts of distilled water, and so on 

 down to any dilution likely to ])e encountered. This will give the 

 resistance corresponding very exactly with known amounts of salt, 

 and will furnish a table for the estimation of the salt content from 

 the resistance of anv water in the area. 



