DURATION OF THE TEST. 115 



ANALYSIS OF THE CINDERS. 



The cinders and ashes produced by the combustion of the 

 coal are collected so as to weigh and sample them. After 

 drying and determining the water the sample is put into a 

 glass tube as with coal. As the quantity of hydrogen is 

 usually very small, it need not be determined, and the 

 calcination for the carbon can be performed in the open air. 

 The following table contains the results of the tests made 

 by Scheurer-Kestner and Meunier-Dollfus on steam-boiler 

 -cinders : 



The proportion of carbon in cinders may be as low as 7 

 per cent, but is usually higher, and 10 to 12 per cent may be 

 called good practice. 



DURATION OF THE TEST. 



A test should continue at least a whole day on account of 

 certain irregularities and causes of error which are constant. 

 The level of the water should be the same at the end of the 

 test as at the beginning, since a slight difference in level 

 means considerable water. 



The condition of the combustion at the time of stopping 

 cannot always be ascertained, and this produces a cause of 

 uncertainty. Another cause is from the temperature of the 

 water in the boiler, and especially in the economizer. On 

 short runs these sources of error cause very faulty results. 



