CHEMICAL SCIENCE. 179 



of the proper temperature, the relative amount of blast to the pig-iron 

 operated upon should be carefully regulated. If too little, the process 

 goes on slowly, and much heat is lost by radiation ; on the other hand, 

 if too much blast is used, there is also a loss from the heat carried off 

 by the air which is forced through the iron before it has effected the 

 desired decomposition. The pressure of the blast must, at all events, 

 be greater than that of the column of iron in the furnace, in order 

 that the bath of molten iron shall be thoroughly penetrated and the 

 whole melted mass set in violent agitation. In Sweden, the pressure 

 of half an atmosphere has in most cases been found sufficient, while in 

 England a pressure equal to one one-half atmospheres has been used. 

 Prof. Tanner, a German scientist, places particular emphasis on the 

 employment of a high pressure with hot blast. He says that if the 

 blast were to be heated to 200 - 300 C., or perhaps even to 500 - 

 600 C., the conversion would unquestionably proceed with great reg- 

 ularity and completeness, and the difficulties in the manufacture of 

 soft bar-iron and steel would be overcome. Further, it is to be borne 

 in mind, that, in order to produce a given variety of steel or iron, the 

 process of conversion must be interrupted whenever the refining has 

 reached the desired point ; this last is determined by observing the 

 character of the gases and sparks which escape from the furnace, very 

 much as is the case in hearth refining ; practice is of course required 

 to be able to determine this point with accuracy. The fracture of the 

 metal serves as a control in sorting the different qualities. The cost 

 for furnace-repairs is much less than was at first anticipated, but the 

 waste product in conversion (equal to 20-30 per cent., when the iron 

 is made into bars) demands consideration, especially as no use has yet 

 been found for this more or less impure product. If, however, we take 

 into consideration the length of time that has been necessarv to bringr 



^j v en 



the puddling process to its- present perfection, w T hile on the other hand 

 Bessemer's process has accomplished so much in so short a time, we 

 have every reason to hope that the day is not far distant when the 

 still remaining difficulties in this process will be reduced to a minimum. 

 Polytechnisches Journal, clxvi. 447. [A wide field is open for the 

 application of Bessemer's process in this country, where pure iron ores, 

 fully equal in quality to those of Sweden and Norway, occur in such 

 abundance.] Silliman's Journal. 



A NEW COMPOUND OF SILICON SENSITIVE TO LIGHT. 



The addition of a new member to a class of bodies is always of in- 

 terest, but the discovery of a new and very sensitive photographic body 

 is of especial value, more particularly, if entirely new ground is opened 

 out by it, and the stranger comes before us as the representative of a 

 new series of elementary bodies hitherto unsuspected of the slightest 

 tendency to photographic change. If we had had to hazard a predic- 

 tion as to the body whence the next photographically sensitive com- 

 pound would be derived, certainly the last substance which would have 

 suggested itself would have been common flint or silica. Until the last 

 few years, silicium, the basis of this, was about the most uninteresting 

 substance in chemistry ; but now, through the researches of Wohler, 

 it bids fair to rival any of the other elements in the number and inter- 

 est of its compounds. This chemist has recently discovered several 



