CERTAIN USEFUL ANALYSES. 195 



carbonate, or in combination with carbonic acid, that 

 being the most common form. If it is not present 

 as carbonate, or if this is in so small quantity as not 

 to show any action with acid, there are still means for 

 its easy and certain detection. To the solution pre- 

 viously rendered alkaline by ammonia, and already fil- 

 tered to separate iron and alumina, is to be added a lit- 

 tle common oxalic acid. If there be even the smallest 

 weighable quantity of lime present, a white powdery 

 precipitate will begin to fall; from the abundance of 

 this, may be estimated roughly the proportion of lime 

 in the soil. 



All.of the above important points, it will be noticed, 

 may be determined without any necessity for expen- 

 sive materials or apparatus, by a person of ordinary 

 intelligence. Easy as these things seem, however, 

 in the description, so many difficulties will be found 

 in practice, as will give the operator some conception 

 of the care and study involved in a complete and de- 

 tailed analysis; one where it is intended to ensure the 

 greatest possible degree of accuracy. 



I have not mentioned any tests for the presence of 

 phosphoric acid, and other of the less abundant sub- 

 stances; because their detection and separation is so 

 difficult, that the inexperienced beginner would only 

 run into every description of error while looking for 

 them. 



It is not a hard matter for the farmer to arrive at 

 the probable value of a marl, with quite a tolerable 

 degree of accuracy. A weighed portion must be 

 taken, and diluted muriatic acid added from time to 

 time, until all effervescence has ceased. The mixture 

 is then boiled, or at least well heated, and thrown 

 upon a fdter. The insoluble residue which remains 

 upon the filter, must be washed clean from acid, dried, 

 and weighed : this is chiefly silica. Its weight, sub- 

 tracted from the original weight taken, will, in mosl 



