APPENDIX C. 561 



lucent solution shows the presence of at least one per cent of humus 

 in the soil ; a deep brown translucent color indicates about one-half of 

 one percent ; while a light brown color clearly shows a deficiency in the 

 soil, and a need of a good green-manure crop. 



Lime. Two grams of fine earth is treated with a little hydrochloric 

 acid, boiled for a few seconds, and ammonia is added to precipitate 

 the iron and alumina ; the whole, with the soil-residue, is quickly thrown 

 on a filter to separate the mass from the lime solution, and washed. 

 After adding ammonium chlorid the lime is precipitated with oxalate 

 of ammonia, and its adequacy for soil-fertility judged of by the turbid- 

 ity of the solution, or the bulk of the precipitate. Or the latter may 

 be filtered off, dried and weighed. We thus obtain a measure of the 

 carbonate and humate of lime present, by comparing it with the pre- 

 cipitate obtained from a soil whose percentage of lime has been cor- 

 rectly ascertained. 



Potash. The determination of potash in the soils requires more time 

 than either of the other ingredients, and is more rarely made by us. 

 Our knowledge of the soils of the State of California obtained through 

 mvny analyses, gives us a clue to those localities where potash would 

 probably be deficient, as well as to those whose soils are generally ex" 

 tremely rich in potash ; the percentages reaching usually from .5 to as 

 much as 1.5 percent and more. 



For the determination, two grams of the fine earth is digested in 

 hydrochloric acid over a steam bath for two days, the insoluble residue 

 filtered off, the filtrate evaporated to dryness to render the silica in- 

 soluble, again filtered and the iron, alumina and lime removed by pre- 

 cipitation with ammonia and oxalate of ammonia and filtration. The 

 filtrate is then evaporated to dryness, the ammonia salts destroyed with 

 aqua regia or driven off by heat, and the alkalies changed to chlorids. 

 Any residue is then filtered off and platin-chlorid added to precipitate 

 the potash, which is separated and determined in the usual way, either 

 by reduction of the platinum by ignition, or by measurement in a 

 Plattner's potash tube. 



Phosphoric AciiL The determination of phosphoric acid is based on 

 the volume of the phospho-molybdate precipitate in a tube made like 

 a Plattner's potash tube, but having a wider interior diameter for the 

 smaller portion (not greater than 3 millimeters), and a length of 50 

 mm. With this diameter, one mm. in height of the precipitate obtained 

 by our short method indicates one one-hundredth of one per cent of 

 phosphoric acid in the soil. The unit of measure must be obtained for 

 36 



