450 



SCIENCE. 



[Vol. IX., No. 223 



mine is wet, and water has to be used on the 

 screens to effect a separation of the dirt from the 

 coal, it is the best and most economical appliance 

 that can be employed. But the greater part of 

 the coal going to market conies from dry mines, 

 where it would be a detriment to the quality of 

 the coal, and a great expense, to use water. 

 The waste water from the jig is also expensive to 

 take care of, as in most localities it is no longer 

 allowable to let it run, with the fine dirt it holds 

 in solution, into the nearest creek, as the sediment 

 will carry a long distance, and deposits itself 

 where it will do harm, and entail a suit for dam- 

 ages. Enough tanks have therefore to be provided 

 to allow all the waste water to thoroughly settle, 

 so that the water and culm can be removed 

 separately. Water itself, or rather the pure 

 article, is both scarce and expensive during a part 

 of each year throughout nearly the whole region. 

 And if mine water is used, as is generally the 

 case, the acid contained in it attacks the iron 

 work of the jig, and makes frequent repairs 

 necessary. 



The principle the jig works on is based on the 

 difference in specific gravity between coal and 

 slate. The two enter the bottom of the jig to- 

 gether, and, by the pulsations of a large plunger 

 in an adjoining compartment, water is forced up 

 through the coal, lifting it, and allowing a fresh 

 supply to come in. The coal is forced to the top 

 and runs off with the water, while the slate, 

 owing to its greater specific gravity, passes out 

 through a separate opening in the bottom. What 

 is needed, in Mr. Ludlow's opinion, is a dry jig, 

 in which this separation will be effected by the 

 use of air instead of water. One of the diffi- 

 culties encountered in getting up such a jig is 

 caused by the care with which coal has to be 

 handled to prevent its chipping or breaking. It 

 cannot be dropped on iron, or wire, or itself, 

 without producing an appreciable percentage of 

 waste. With the most approved rolls, the loss in 

 rebreaking any size to a smaller one amounts to 

 from ten to fifteen per cent. While the differ- 

 ence in specific gravity between coal and slate of 

 the same-sized pieces is very great, still trouble 

 would be experienced in any separation by an air- 

 current with flat pieces of both slate and coal, 

 on which the action of the air would vary, ac- 

 cording as it acted on the edge or the whole 

 side. The man who invents a successful dry jig, 

 that will stand the test of actual trial, will un- 



doubtedly make a very handsome thing by it. 

 Not to be too cumbersome, a single jig should not 

 have a greater capacity than five hundred tons per 

 day ; and, as the shipping capacity of the anthra- 

 cite region is about two hundred thousand tons 

 per day, it would take about four hundred to 

 supply the trade. 



Peofessor Vaughan of Michigan univeesity 

 has been engaged in the study of the chemistry 

 of tyrotoxicon, the principle discovered by him in 

 poisonous cheese, and which he believes to have 

 been responsible for a number of cases of poison 

 due to ice-cream. Professor Vaughan concludes 

 from his studies that tyrotoxicon and diazobenzol 

 are identical. To a large eat a small bit of diazo- 

 benzol nitrate was given, dissolved in water. In 

 a few minutes the animal began retching, and in 

 three-quarters of an hour it vomited freely, and 

 later was purged. The stomach, when opened, 

 was found to contain a frothy fluid, and its mu- 

 cous membrane was blanched. Thus, not only 

 were the symptoms identical with those of tyro- 

 toxicon, but the post-mortem appearance was the 

 same as that observed in cats poisoned with tyro- 

 toxicon obtained from cheese, milk, and ice-cream. 

 From some oysters which poisoned nearly seventy 

 people in Michigan lately. Professor Vaughan ob- 

 tained the tests for diazobenzol. The symptoms 

 produced by the oysters were identical with those 

 observed after eating poisonous cheese, ice-cream, 

 and milk. It is altogether likely that the active 

 agent in all those foods which when partly pu- 

 trid produce the same group of symptoms, is 

 diazobenzol, probably combined with different 

 acids. Professor Vaughan is now experimenting- 

 with the hope of ascertaining the nature of the 

 micro-organism which produces this poison, but 

 is not yet ready to make any definite report. It 

 seems to be a germ which develops best in the 

 absence of ^air, or with only a limited supply of 

 air. 



We are now approaching the season when 

 the attention of teachers and pupils alike is turned 

 toward the important matter of examinations. 

 Keview-work is begun, and there is a general 

 arranging and polishing-up of knowledge in an- 

 ticipation of the annual test. Since examinations 

 play so important a part in our educational in- 

 stitutions from primary school to college, it is 

 fitting that they should be the subjects of special 

 thought and attention. For this reason we print 



