Otto Folin and Vintila Cioicalteu investigated the determination of tyrosine and tryptophan in proteins using the phenol reagent. They found that the Folin-Looney methods for these determinations had limitations, particularly due to the instability of the phenol reagent and the formation of blue color from the reagent itself. They developed a new colorimetric method for estimating tyrosine in protein hydrolysates, which involved using a specific amount of phenol reagent to achieve accurate results. They also discussed the hydrolysis of proteins with alkalies, noting that barium hydroxide was the only alkali that did not destroy tryptophan. They described a new method for determining tryptophan using Millon's reaction, which provided more accurate results than the Folin-Looney method. They also provided detailed procedures for the preparation of pure mercuric sulfate, which is essential for these determinations. The study concluded that the new methods provided more accurate and reliable results for the determination of tyrosine and tryptophan in proteins.Otto Folin and Vintila Cioicalteu investigated the determination of tyrosine and tryptophan in proteins using the phenol reagent. They found that the Folin-Looney methods for these determinations had limitations, particularly due to the instability of the phenol reagent and the formation of blue color from the reagent itself. They developed a new colorimetric method for estimating tyrosine in protein hydrolysates, which involved using a specific amount of phenol reagent to achieve accurate results. They also discussed the hydrolysis of proteins with alkalies, noting that barium hydroxide was the only alkali that did not destroy tryptophan. They described a new method for determining tryptophan using Millon's reaction, which provided more accurate results than the Folin-Looney method. They also provided detailed procedures for the preparation of pure mercuric sulfate, which is essential for these determinations. The study concluded that the new methods provided more accurate and reliable results for the determination of tyrosine and tryptophan in proteins.