In this case an excess of sulphuric acid was used. After the oxalic acid had all been decomposed or driven off the mass turned black and became very pitchy. Nothing could be done with it so it was thrown away.
In this case an excess of ortho toluidine was used. The red dyestuff was formed in great amount and very easily. The temperature was kept below 195 to lose none of the toluidine which boiled at 199.
This method gave the best results and is the one employed in the preparation of all the material used in the thesis. Equal weights of ortho toluidine and sulphuric acid (100gms. of each were used; 100gms. of ortho toluidine is 108cc., and 100gms. of sulphuric acid (s. g. 1.84) are 56cc.), were mixed and baked at 190-195 until a sample would dissolve in ten per cent sodium hydroxide solution to give a clear solution; this took one and a half hours. The mixture at first melts in the solution of the sulphate and sulphuric acid formed by the heat of combination; as heating is continued it gradually becomes solid and finally very hard; it has become gray in color. When it is perfectly dry a test is made to see if it dissolves in sodium hydroxide giving a clear solution. If so, sulphonation is complete. By using an oven with a glass door the reaction mixture can be watched and the completion of the baking observed. However the test for complete solubility should always be made. The addition of powdered oxalic acid to the reaction mixture did not seem to be of advantage, because no visible reaction commenced until this had been driven off or decomposed. It is usually added in producing sulphonic acids by baking the sulphates of the amines to increase the porosity of the mass and thus facilitate removal of the product. However here the only effect seemed to be to retard the reaction, as the product was the sane hard grayish mass as without the acid, and it was just as difficult to dig it out. It took an hour longer to complete the reaction with the addition of the oxalic acid.
The best results were obtained when the temperature of the oven was kept at 193, although five degrees variation did not appreciably affect the product. A lower temperature gives little or no action, while a higher one drives off the ortho toluidine and also seems to favor the formation of the red dyestuff.