cao 16 mgo 4 na sub 2 o 4______________________________________ a glass of this composition has a high young 39 s modulus of elasticity above 7500 kg mm 2 two starting liquids are made up the first is made by mixing in the liquid phase tetraethoxysilane si oc 2 h 5 4 which may be prehydrolised aluminium butylate al oc 4 h 9 3 and boron butylate b oc 4 h 9 3 and the second is a solution in methanol of methylates of magnesium mg och 3 2 calcium ca och 3 2 and sodium naoch 3 the alcoholates are used in molar proportions corresponding to the proportions of the oxide forming elements in the glass composition these alcoholates are hydrolysed by the addition of water in a molar proportion of h 2 o alcoholates 3 1 in the presence of acetic acid by hydrolysis and polycondensation of the mixture of the starting liquids a gel is formed after heating between 80 u00b0 and 250 u00b0 c to reduce the volatile content in the gel to about 5 by weight such volatile content being mostly water and alcohol a powdery gel is obtained this powder whose grains have a mean size of about 9 u03bcm is injected into the flame of a burner to effect vitrification and spherulization at a rate of 500 kg hour the burner is fed with fuel natural gas at a rate of 130 nm 3 hour and with air at a rate of 15000 nm 3 hour the hottest.