158 EXPERIMENTS WITH PLANTS 



ride (eoimuoa salt) and 3.3 grams sodium sulphate^ (Glauber's salt). 

 This gives a content in the soil of one-tenth of one per cent soda, two- 

 tenths of one per cent common salt and three-tenths of one per cent 

 Glauber's salt: these are all excessive and hurtful amounts, and a soil 

 which contains so much of either is not suitable for ordinary crops. 

 Place filter paper in a funnel and put the soil in it; add 20 cc. of water 

 and let it leach through into a test-tube; test with litmus paper. The 

 rapidity with which the paper turns blue indicates the amount of black 

 alkali or sodium carbonate: if it quickly turns deep blue it indicates an 

 excessive amount (one-tenth of one per cent or more: if it turns blue 

 very slowly it indicates a lesser amount). Dilute some of the filtered 

 liquid with one, two and three volumes of water and test with litmus 

 paper. Save some of the filtered liquid to be used as a standard of com- 

 parison on future occasions. Take a portion of the filtrate and test for 

 common salt as follows: Add a few drops of nitric acid (chemically pure) 

 and then a drop or two of a 1.7 per cent solution of nitrate of silver 

 (this is made by adding 1.7 grams to 100 cc. of water); a curdy pre- 

 cipitate^ shows an excessive amount of salt (two tenths of one per cent 

 or more) and from this we may find, in testing soils, all amounts down 

 to a trace which gives only a slight milkiness on the addition of nitrate 

 of silver. Take another portion of the filtered liquid, and test for 

 Glauber's salt, as follows: add a few drops of hydrochloric acid (chemi- 

 cally pure), heat and add a few drops of barium chloride to the hot 

 solution: transfer to the funnel described above and measure the amount 

 of precipitate:^ this will of course indicate in the present case a content 

 in the soil of three- tenths of one per cent, which is an excessive and 

 injurious amount. 



By these simple tests which, although only rough approximations, 

 nevertheless serve admirably for practical purposes, we may, after our 

 standards of comparison are once established, in a few moments learn 

 whether a given soil is deficient in any of the important elements of 

 plant-food and whether it contains injurious amounts of alkali. 



1 Allowance has been made for water of crystalization. 



2 The precipitate is silver chloride. 

 ^The precipitate is barium suli)hate. 



