the chrome ore is a beneficiated product with a major portion of the silica removed . the magnesite is extremely pure , containing up to 99 percent mgo . typical chemical analyses of the raw materials used in the refractory of this invention are shown in table i . the silica content of the chrome ore may vary from 1 . 7 to 2 . 7 weight percent , but the composition shown is typical . two types of magnesite are shown and both are acceptable . table i______________________________________ chrome ore x magnesite a magnesite b______________________________________chemical analysis ( calcined basis ) silica ( sio . sub . 2 ) 2 . 0 % 0 . 13 % 0 . 75 % alumina ( al . sub . 2 o . sub . 3 ) 10 . 7 0 . 09 0 . 18titania ( tio . sub . 2 ) 0 . 13 0 . 01 0 . 01iron oxide ( fe . sub . 2 o . sub . 3 ) 14 . 8 0 . 40 0 . 18chromic oxide ( cr . sub . 2 o . sub . 3 ) 56 . 9 -- -- lime ( cao ) 0 . 10 0 . 68 0 . 48magnesia ( mgo ) 15 . 7 98 . 70 98 . 41total analyzed 100 . 06 % 100 . 00 % 100 . 00 % ______________________________________ for comparative purposes , typical chemical analyses of philippine chrome ore and refractory grade magnesite that are representative of materials used in the chrome - magnesite brick of the prior art are listed in table ii . table ii______________________________________ philippine lump chrome ore magnesite c______________________________________chemical analysis ( calcined basis ) silica ( sio . sub . 2 ) 6 . 00 % 3 . 0 % alumina ( al . sub . 2 o . sub . 3 ) 27 . 0 0 . 4titania ( tio . sub . 2 ) 0 . 21 & lt ; 0 . 01iron oxide ( fe . sub . 2 o . sub . 3 ) 14 . 9 0 . 5chromic oxide 31 . 4 & lt ; 0 . 01 ( cr . sub . 2 o . sub . 3 ) lime ( cao ) 0 . 50 0 . 9magnesia ( mgo ) 19 . 5 95 . 0total analyzed 99 . 51 % 99 . 8 % ______________________________________ the chrome ore is basically sized to pass through a 4 mesh screen , although a portion may be added as ball milled fines . the magnesia will be basically added as ball milled fines either as straight magnesite or as a ball milled preburned mixture of magnesia and chrome ore , often referred to as &# 34 ; bats &# 34 ;. in certain cases , magnesia may be added to the batch as a coarse fraction . however , there must always be enough magnesia in the ball milled fraction to insure reaction to spinel minerals by the r 2 o 3 constituents in the chrome ore . this results in good burning stability and slag resistance . a series of four chrome - magnesite brick designated mixes a , b , c and d were made with varying ratios of chrome ore x and magnesite a as shown in table iii . in addition , data for two conventional chrome - magnesite brick that are representative of prior art are listed in the table as mixes e and f . the brick were made from size graded batches using common brickmaking procedures , such as adding a bonding agent such as calcium lignosulfonate , pressing the brick at 12 , 000 psi , drying the brick and then burning them in a tunnel kiln . table iii__________________________________________________________________________ conventional low - fired chrome - magnesite brickmix designation : a b c d e f__________________________________________________________________________chrome ore / magnesite ratio : 95 / 5 90 / 10 80 / 20 70 / 30 80 / 20 74 / 26mix composition : chrome ore x - 4 /+ 10 mesh 35 % 35 % 35 % 35 % -- -- 010 /+ 28 mesh 17 17 17 17 -- -- - 28 mesh 28 28 28 18 -- -- ball milled fines 15 10 -- -- -- -- magnesite a - 28 mesh -- -- -- 11 -- -- ball milled fines 5 10 20 19 -- -- philippine lump chrome ore - 4 /+ 8 mesh -- -- -- -- 24 % 24 % - 8 /+ 28 mesh -- -- -- -- 26 26 - 28 mesh -- -- -- -- 30 24magnesite c ball milled fines -- -- -- -- 20 26burning temperature , ° f . : 3130 3130 3130 3130 2800 2800bulk density , pcf : 217 215 211 206 193 193drip slag test at 2650 ° f . ( reducingconditions using 1600 grams ofcopper convertor slag ) volume of erosion in cu cm : bloated bloated 21 16 30 41chemical analysis ( calcined basis ) silica ( sio . sub . 2 ) 1 . 91 % 1 . 82 % 1 . 63 % 1 . 44 % 5 . 6 % 5 . 0 % alumina ( al . sub . 2 o . sub . 3 ) 9 . 69 9 . 19 8 . 58 7 . 52 22 . 5 20 . 9iron oxide ( fe . sub . 2 o . sub . 3 ) 14 . 56 13 . 82 11 . 92 10 . 5 12 . 1 10 . 5chromic oxide ( cr . sub . 2 o . sub . 3 ) 53 . 20 50 . 40 45 . 52 39 . 8 26 . 8 25 . 2lime ( cao ) 0 . 12 0 . 15 0 . 22 0 . 28 1 . 4 1 . 1magnesia ( mgo ) 19 . 76 23 . 92 32 . 3 40 . 6 31 . 6 73 . 3total analyzed 99 . 24 % 99 . 30 % 100 . 17 % 100 . 14 % 100 . 0 % 100 . 0 % __________________________________________________________________________ mixes a , b , c and d were burned at the relatively high temperature of 3130 ° f . while mixes e and f , the conventional brick , were only burned at 2800 ° f . the higher burning temperature for mixes a , b , c and d was made possible by the controlled chemistry described earlier . more specifically , the substantially lower silica content and control of the ratio of chromic oxide to the oxides of iron and aluminum to greater than 2 to 1 make it possible to burn mixes a , b , c and d at the higher temperature . the higher silica contents and low ratio of chromic oxide to the oxides of iron and aluminum make it necessary to burn mixes e and f at the lower temperature . because of their favorable chemistry , mixes a , b , c and d can be burned at 3130 ° f . without resulting in the brick sticking together . brick from mixes e and f , because of their unfavorable chemistry , stick together if burned at 3130 ° f . the ability to burn chrome - magnesite brick at temperatures as high as 3130 ° f . and the controlled chemistry described earlier results in brick with improved slag resistance . the slag resistance of these mixes was tested using astm test method c 768 . in the test , 1600 grams of copper converter slag were dripped onto the brick at 2650 ° f . after cooling , the cubic centimeters of brick removed by erosion were measured . the chemistry of the copper converter slag used in this testing is listed in table iv . table iv______________________________________ copper converter slag______________________________________chemical analysis ( calcined basis ) silica ( sio . sub . 2 ) 27 . 7 % alumina ( al . sub . 2 o . sub . 3 ) 5 . 92titania ( tio . sub . 2 ) 1 . 79iron oxide ( fe . sub . 2 o . sub . 3 ) 56 . 4chromic oxide ( cr . sub . 2 o . sub . 3 ) 0 . 52manganese oxide ( mno ) 0 . 27copper oxide ( cuo ) 4 . 2lime ( cao ) 2 . 36magnesia ( mgo ) 0 . 43total alkalies 0 . 41total analyzed 100 . 0 % ______________________________________ as is evident from table iii , mixes c and d , made according to this invention , had substantially lower erosion in the drip slag test than mixes e and f , the conventional chrome - magnesite brick . in addition , slag testing results on mixes a and b illustrate the unsuitability of high fired chrome - magnesite brick made with insufficient magnesia . both mixes a and b were severely bloated as a result of the slag test . while a preferred embodiment of the invention has been described , the invention should not be limited thereto , but may be otherwise embodied within the scope of the following claims .