In his final letter Jekyll explains why Hyde became the more powerful half of his personality. Describe.

The final chapter presents a transcription of Jekyll's confession letter to Utterson. Jekyll begins by claiming that at birth he was fortunate to have a large inheritance, health, and a hardworking nature. A strong idealist, Jekyll maintained social respect while keeping his more questionable vices secret. When he reached adulthood, Jekyll found that he was living two lives, one of the utmost respectability and social graces, and the other of hidden pleasures and dark underpinnings. As a scientist, Jekyll decided to examine the dual nature of man through mystical study that Lanyon found particularly offensive. In the latter, Jekyll insists, "man is not truly one, but truly two," and he explains how through his research he hoped to separate each side.

After years of work, Jekyll eventually created a chemical solution that would allow him to complete his work. Jekyll purchased a large quantity of salt for his final ingredient, and resolved to drink the concoction, knowing full well that he was putting his life in danger. The drink caused him pain and nausea, but as these feelings passed, Jekyll began to examine the results of his work. In fact, he felt strong, sensual and wild and he noticed that his body had changed. His hands were smaller and gnarled looking, and his clothes were suddenly far too large, which led him to conclude that his alter ego, which he later named Edward Hyde, was a small, dwarfish man. Jekyll reasoned that this identity was physically smaller because it represented his evil side which had previously been repressed and carefully controlled.

Jekyll looked in the mirror to examine his new identity and rather than feeling the repulsion that every other character in the book noted, Jekyll felt "a leap of welcome." In truth, Jekyll enjoyed living as Hyde. He was free to behave in a less honorable manner and partake in the darker side of London. Through Hyde, Jekyll could live a dual life, where he could both maintain respectability and indulge his most base desires. Jekyll established a residence for Hyde, in the cabinet room off his laboratory that had its own street entrance. And, after the incident with the young girl that Enfield witnessed, Jekyll opened a bank account for Edward Hyde in order to avoid suspicion. With all this freedom and power, Hyde began to gain strength. Jekyll felt no remorse at his alter ego's behavior, but did try to right any wrongs Hyde caused.

Jekyll's dual life was going perfectly as planned until two months prior to the murder of Sir Danvers Carew. One night, Jekyll transformed into Hyde involuntarily, while sleeping. Suddenly, Jekyll realized that he was in great danger of being trapped in the body of Hyde permanently, and that some aspect of the experiment had moved beyond his control. For two months entire months, Jekyll lived only as himself. However, he soon felt the need to free his evil side, and in a moment of extreme weakness, took the potion. Hyde emerged, and after months of repression, was out for blood. On this fateful night, Hyde murdered Sir Danvers Carew, beating him to death with one of Jekyll's canes. Of course, Hyde felt no guilt, but even before he had completely transformed back into himself, Jekyll was asking God for forgiveness. Again, Jekyll resolved to never make another transformation. Over the next few months, Utterson had noticed Jekyll's improved and more sociable behavior. It seemed as though he had freed himself of a great weight.

Just as before, Jekyll grew bored with his pure and virtuous life, and gave in to his baser urges, albeit in his own identity. However, even though he did not transform himself into Hyde, partaking in evil activity at all strengthened Hyde inside of him. Thus, Jekyll suffered another spontaneous transformation, this time in a park outside of his home. Afraid he would be captured by the police, and unable to return to his home because the servants would see him and report him, Hyde sent for Lanyon's assistance. From that night forward, Jekyll had to take double doses of the potion every six hours to avoid unintentionally waking up as Hyde. When the drug wore off, Hyde would appear, and it was the beginnings of such a transformation that Enfield and Utterson witnessed at the cabinet window.

In his final days and hours, Jekyll explains that Hyde grew increasingly stronger as Jekyll began to fade away. To make matters worse, Jekyll's supply of potion salt was running out. He ordered more, only to discover that the new salt was not effective. After ordering the most pure salt possible, Jekyll finally realized that the original order must have contained an unknown impurity that was actually the key potion ingredient. Without any more of the original salt, there was no way for Jekyll to discover what that secret ingredient was. Jekyll realized he had no choice but to transform permanently in to Hyde. After taking the last dose of potion, Jekyll, as himself, sat down to compose a new will and letters to Utterson to explain the entire situation. While writing, Jekyll claims he cannot be sure how Hyde will react when the rest of the world discovers him. But, he states that without a doubt, when Utterson reads the letter, Henry Jekyll will have ceased to exist.