90 Samples and Sampling [1 28-131 



PREPARATION IN THE LABORATORY 



128. For preparing the samples for analysis, the following 

 equipment is necessary : 



A large iron mortar and pestle. The mortar should be 

 about 12 inches in diameter. 



A steel spatula, having a blade 10 inches long by 1^ inch 

 broad. An ordinary butcher's broad-bladed knife will do 

 excellently. 



A set of sieves having meshes varying from 4 to 16 per linear 

 inch. Sieves made with wire gauze are often very difficult to 

 clean, which leads to much waste of time. Perforated zinc is 

 much preferable, and may be obtained with different sized 

 holes. 



Some form of mill. A coffee-mill will do very well, if 

 arranged so that it may be taken to pieces ; otherwise it will be 

 found impossible to clean it thoroughly. 



A number of sheets of brown paper. 



129. The preparation in the laboratory sampling room 

 varies according to the texture of the sample. The substances 

 ordinarily occurring may be classed under the following heads : 



130. Liquids. — Water, milk, sewage, phosphoric acid, &c. 

 These need no preparation, as they may be shaken up and 

 analysed at once. 



131. Hard Minerals. —Limestone and mineral phos- 

 phates. Break up in an iron mortar until the whole of the 

 sample may be passed through a sieve with J-inch meshes. 

 Spread it out on a piece of brown paper, and select from diffe- 

 rent parts of the heap sufficient to fill a sample bottle (10-oz. 

 wide-mouthed bottles of common glass are best). A finer 

 sample must be prepared by selecting in the same way about 

 20 grams, and grinding up in an agate mortar until the whole 

 will pass through a sieve having 90 meshes to the linear inch. 



