136 Commercial Gardening 



loss of C0 2 gas. 44 parts of the gas represent 100 parts of calcium carbonate 

 that was present. This assumes that there is no magnesium carbonate 

 present. 



Humus. In estimating the humus, 10 gm. of dried soil are taken 

 and washed on the filter paper with a 1-per-cent solution of hydrochloric 

 acid till free from calcium salts. It is then well washed with hot, distilled 

 water till free from acid, and washed into a long stoppered cylinder with 

 500 cub. cm. of 4-per-cent ammonia solution. It remains in the solution 

 twenty -four hours, allowing the cylinder to lie in as nearly a horizontal 

 position as is possible without allowing the stopper to leak, and is well 

 shaken at intervals. The cylinder is then stood upright for twelve 

 hours to allow the whole to settle to the bottom. The solution is then 

 filtered, and 100 cub. cm., representing 2 gm. of soil, are taken and 

 evaporated to dryness over the water bath. The dish is then placed in 

 the water oven for a few minutes, to dry off any adhering moisture, 

 and weighed. After weighing, it is incinerated until all the organic 

 matter has burned off. The dish is allowed to cool in the desiccator 

 and the weight again taken. The difference in the weights before and 

 after incineration gives the humus. 



Magnesia. This is estimated by boiling 5 gm. of dried soil with 25 

 cub. cm. of concentrated hydrochloric acid, and evaporating to dryness over 

 a water bath. The residue is moistened with concentrated sulphuric acid, 

 then treated with a mixture of 10 cub. cm. of hydrochloric and 10 cub. cm. 

 of water, warmed, filtered while hot, the filter paper being well washed, 

 and the filtrate treated with an excess of ammonia, boiled, allowed to cool, 

 and filtered. The filtrate is neutralized with acetic acid and treated with 

 ammonium oxalate (about 20 cub. cm.) to remove calcium, and again fil- 

 tered. The filtrate is evaporated down and treated with successive 5-cub.- 

 cm. lots of concentrated nitric acid to eliminate ammonia salts. As the 

 liquid by this time has evaporated down to a small bulk, it is diluted to 

 about 200 cub. cm., treated with ammonium phosphate, and allowed to 

 stand for twelve hours. It is then filtered and washed with dilute am- 

 monia, dried in the steam oven, and incinerated in a crucible and weighed. 

 From the weight of magnesium pyro- phosphate obtained the magnesia 

 can be calculated as MgO. 1 part of magnesium pyro -phosphate = 36 

 parts of magnesia oxide. [c. P. c.] 



