594 ' Mr. Alexander Siemens [April 23, 



bars of tantalum springs can be bent, as the specimens on the table 

 show. 



Another use made of tantalum is as material for writing pens, 

 manufactured in the usual way. 



When it was first offered for this purpose, it was found that the 

 material could not pass the test prescribed for pens made of steel. 



These are pressed by a weight of 180 grammes on writing paper, 

 which is moving at the same speed as ordinary writing, and while 

 10 km. (6 J miles) of paper are passing, the loss by abrasion must 

 not exceed 0*7 mg. (0*01 grains). 



At first the tantalum pens lost more than double the permitted 

 weight, but it was found that slightly oxidising the surface of the pens 

 hardens them so much, that they only lose * 8 mg. by the 10 km. test. 



By weight this is still more than permitted for steel pens, but 

 having regard to the specific weights of the two substances, the 

 actual volumetric abrasion of the tantalum pen is the lesser of the 

 two. 



Although only the surface of the pens had been oxidised, it was 

 found that the rate of abrasion remained the same for the whole 

 length of 10 km., when it was expected that this rate would increase 

 materially after the skin of oxide had been ground off. 



Advantage was taken of this circumstance when an inquiry was 

 received from India whether it would be possible to manufacture 

 cataract knives for oculists out of tantalum. 



The qualities demanded of such a knife are that its blade should 

 be— 



1. Intensely hard, so as to be able to acquire a very sharp edge 

 of great smoothness, and to retain this fine edge for a long time. 



2. Yery tough without any tendency to bend. 



3. Chemically and mechanically stable, so that it can be easily 

 sterilised and that it is not liable to rust. 



4. Capable of acquiring a high polish. 



Manufacturing such a blade out of pure tantalum and slightly 

 oxidising it, before polishing it, appears to fulfil these stringent con- 

 ditions, but as the knife which is on the table has not yet been 

 actually tried for an operation, it can only serve to demonstrate the 

 similarity of tantalum to steel for such purposes. 



Another field for the application of tantalum may be found in 

 the supply of dental instruments, owing to its immunity from chemical 

 changes, but beyond showing two cases of such appliances, there is 

 no necessity to go further into details. 



While possessing all these qualities of a true metal, tantalum has 

 some others which rather limit its usefulness. 



When heated to a dull red it absorbs gases greedily, especially 

 hydrogen and nitrogen, and by combining with them it loses its 

 tensile strength and becomes brittle. 



Here are three pieces of tantalum wire taken from the same coil ; 



