3 8o 



THE POPULAR SCIENCE MONTHLY. 



and the bricks it was intended to cement 

 become loose. The remedy for this evil is 

 the employment of lime from non-magne- 

 sian limestone. 



This explanation of the phenomenon of 

 incrustation is pronounced to be the cor- 

 rect one by the editor of the Polytechnic 

 Review, who also approves Mr. Traut- 

 wine's proposed remedy for the evil. At 

 the same time he offers, on theoretical 

 grounds, a simpler remedy, which he pro- 

 poses to have subjected to the test of prac- 

 tical experiment. This remedy is the addi- 

 tion of a small quantity of baryta to the wa- 

 ter used for tempering the brick-clay. The 

 rationale of this process we will state as 

 briefly as possible, mainly in the author's 

 own words : The incrustation being due to 

 the process of soluble sulphates, caused by 

 the decomposing action of sulphuric acid on 

 the magnesia and lime silicate in the clay, 

 the presence of a small amount of free ba- 

 ryta would either altogether prevent or at 

 least greatly reduce the amount of this de- 

 composition. The baryta, having a strong 

 affinity for the free acid, would seize upon it, 

 and with it form insoluble sulphate of baryta. 

 Even though the free baryta did not alto- 

 gether prevent the formation of the soluble 

 sulphates, it is safe to assume that there 

 will be present in the finished brick suffi- 

 cient uncombined baryta to decompose and 

 cement into insoluble barium sulphate such 

 soluble magnesia and lime sulphates as may 

 have been formed during the process of burn- 

 ing, so soon as these sulphates are dissolved 

 by moisture. A like addition of baryta to 

 mortar after it is prepared for use may rea- 

 sonably be expected to check the tendency 

 to efflorescence, except of course where the 

 mortar, as in chimneys, is continuously ex- 

 posed to the action of sulphurous vapors. 



Am Interesting Experiment. A simple 

 experiment, devised by Prof. A. M. Mayer, 

 illustrates in a very effective way the action 

 of the forces of attraction and repulsion on 

 bodies freely moving in a plane, and serves 

 to give clearness to our conceptions of 

 molecular action. He takes a number of 

 needles, of the size known as " number 6," 

 and magnetizes them, giving to all the points 

 the same polarity, say north. Then each 

 needle is driven into a small cork float, so 



that it will keep the upright position in 

 water, the eye just coming through the top 

 of the float. If, now, three of the needles 

 be dropped into a bowl of water, and the 

 north-pole of a rather large cylindrical mag- 

 net be brought slowly down over them, the 

 mutually repel lant needles are made to ap- 

 proach one another, and then arrange them- 

 selves thus . ' . Raise the magnet, and the 

 needles go farther apart ; lower it, and they 

 come together again, the three needles al- 

 ways holding their places at the vertices of 

 an equilateral triangle. Add needles suc- 

 cessively, and the following arrangements 

 will be seen, viz. : 



With 4 needles 



or 



The needles can be made to assume the 

 arrangements shown in the second column, 

 but these figures are not stable. So long as 

 the magnet is held directly over them, the 

 needles will remain in the positions indi- 

 cated ; but raise it, so as to let the needles 

 go apart, and then bring it down again 

 quickly, and in all probability the figure 

 given in the first column will be the result. 

 Prof. Mayer has obtained the figures up to 

 the combination of twenty needles. He 

 adds, in a note to the American Journal of 

 Science : " These experiments can be varied 

 without end. It is certainly interesting to 

 see the mutual effect of two or more vibrat- 

 ing systems, each ruled more or less by the 

 motions of its own superposed magnet ; to 

 witness the deformations and decomposi- 

 tions of one molecular arrangement by the 

 vibrations of a neighboring group ; to note 

 the changes in form which take place when 

 a larger magnet enters the combination, and 

 to see the* deformation of groups produced 

 by the side action of a magnet placed near 

 the bowl." 



Experiments with the Electric Light. 



A public exhibition was recently made in 

 Cleveland, Ohio, of an electric-light machine 



